RPSC Programmer Paper-1 Solved Questions

[ Option D ]

Two-Phase Locking (2PL) protocol, which is used for concurrency control in database systems, has the problems of deadlock and cascading rollback.

• Deadlocks occur because transactions may wait indefinitely for locks held by other transactions, causing a cycle of waiting and thus freezing progress.
• Cascading Rollback happens if a transaction fails and rolls back, causing other transactions dependent on its uncommitted data to also roll back, leading to wasted resources and inefficiency.

[ Option A ]

A Cartesian Product between two relations (tables) pairs every row of the first table with every row of the second table. So the total number of tuples is:
Total Tuples = (Number of tuples in X) × (Number of tuples in Y)
Here, Number of tuples in X = 4 and Number of tuples in Y = 3. This means every row of X will pair with every row of Y, producing 4×3 = 12 total tuples.

[ Option C ]

Given the relation R(A, B, C, D) with functional dependencies:
A → B
B → C
C → D
Primary Key: A
Check for BCNF:
A relation is in Boyce-Codd Normal Form (BCNF) if for every functional dependency X→Y,  X is a candidate key or super key.
So, BCNF ensures that each non—key (non—prime) attributes is dependent only on the candidate key.
A→B: A is the primary key (Super Key): Satisfy BCNF condition.
B→C: B is not a Super Key : Violates BCNF condition.
C→D: C is not a Super Key : Violates BCNF condition.
Check for 3NF:
The relation is in 3NF if there is no transitive dependency i.e., no non—prime attribute can determine another non—prime attribute.
A→B: A is the prime attribute : Satisfy 3NF condition.
B→C: Both B and C are non—prime attributes : Violates 3NF condition.
C→D: Both C and D are non—prime attributes : Violates 3NF condition.
Check for 2NF:
The relation is in 2NF if there is no partial dependency i.e., no proper subset of candidate key can determine the non—prime attribute. 
The relation is at least in 2NF, if key contains only one attribute (here A is primary key, only one attribute no subset possible), then there is no partial dependency because one attribute has no subset. So, the relation is in 2NF. Among the given options the correct answer is The relation is not in BCNF.

[ Option B ]

Concurrency Control in a database ensures that when multiple transactions run at the same time, they do not interfere with each other. Its main goal is to maintain correctness, consistency, and isolation so that the final result remains the same as if transactions were executed one by one.
When we check concurrency control protocols, we look for two important properties:

• Conflict Serializability: The schedule should behave like a correct serial order.
• Freedom from Deadlock: Transactions should not end up waiting for each other forever.

Two Phase Locking (2PL) ensures conflict serializability by enforcing that transactions lock data in two phases (growing and shrinking), but it does not guarantee freedom from deadlock. The deadlocks can still occur in 2PL.
Timestamp Ordering Protocol guarantees both conflict serializability and freedom from deadlock because it assigns timestamps to transactions and schedules operations based on these timestamps, avoiding cyclic waits and deadlocks.
Multiple Granularity Protocol primarily helps reduce lock overhead and increase concurrency by using locks at different levels of granularity, but it does not guarantee deadlock freedom by itself. The deadlock can still occur.

[ Option C ]

In relational algebra, the set-difference operation (−) allows us to retrieve tuples that are present in one relation but not in another. It is written as R−S, returns all tuples that are in R but not in S.
This operation requires both relations to be Union-Compatible, meaning they must have the same set of attributes with compatible domains.

[ Option D ]

An Index in a database is a special data structure that helps the system locate records quickly without scanning the entire table.
Primary Indices correspond to the sequence of the data file itself, meaning the index key and the file are ordered the same way.
Secondary Indices have a search key order that is different from the sequential order of the data file. This allows access to data organized by non-primary keys, where the actual data storage is unrelated to the index ordering.

[ Option B ]

The primary advantage of setting up a DMZ (Demilitarized Zone) using a firewall is to create multiple zones of trust within a network, which enhances security. A DMZ acts as a buffer zone between the public Internet and the internal private network, isolating public-facing servers (such as web, email, and DNS servers) from sensitive internal resources. This setup allows external users to access services in the DMZ while preventing direct access to the internal network.

[ DELETE ]

[ Option A ]

A scrambler is used in line coding schemes to modify the original data before transmission.

• To remove long sequences of 0s or 1s which can cause synchronization problems.
• To make the transmitted data appear random, even if the original data has patterns.
• Helps in maintaining clock synchronization between sender and receiver.

[ Option C ]

In Circuit Switching, a dedicated physical path (circuit) is created between the sender and receiver before communication starts. This path remains reserved for the entire duration of the call.

• Each connection gets its own separate path.
• The path cannot be used by anyone else until the communication is finished.
• This is why circuit switching is used in traditional telephone networks.

So, when multiple users communicate at the same time, each user gets a separate circuit.

[ Option B ]

The Domain Name System (DNS) is like the phonebook of the internet. It helps us convert easy-to-remember domain names into numerical IP addresses that computers use to communicate. DNS makes browsing the internet simple and user-friendly.
There are two types of DNS lookups:
Forward Lookup: This converts a domain name to an IP address using A or AAAA records.
Reverse Lookup: This converts an IP address back to a domain name using a PTR (Pointer) record. It helps in verification, logging, and network troubleshooting.

[ Option C ]

The Fragment Offset field in the IPv4 header is 13 bits long. In the IPv4 header, the Fragment Offset field is used to indicate the position of a fragment in the original packet when fragmentation occurs.

• It is measured in units of 8 bytes, allowing the reassembly of fragmented packets.
• This 13-bit field supports offsets from 0 to 8191, which multiplied by 8 equals a maximum byte offset of 65,528.
• This field, together with the More Fragments (MF) flag, helps in fragment reassembly at the destination.

[ Option D ]

In embedded SQL, we write SQL statements inside a host programming language like C, Java, or COBOL. When we want to fetch data from a table and store it directly into host variables, we use the SELECT INTO statement.
The SELECT is used to read data from a table.
The INTO is used to store the fetched values into host language variables.
EXEC SQL SELECT column_name INTO :host_name FROM table_name WHERE condition;

E.g.:
Host variables in C:
char student_name[50];
int student_marks;
Embedded SQL SELECT INTO:
EXEC SQL SELECT name, marks
     INTO :student_name, :student_marks
     FROM Student
     WHERE roll_no=101;

[ Option D ]

The Address Resolution Protocol (ARP) is used for finding the MAC address that corresponds to a given IP address within a Local Network.
When a device wants to communicate with another device on the same network, it needs the MAC address (Physical Address) of the destination device to actually send the data.
ARP helps in this process by broadcasting a request with the target IP address to all devices on the network. Only the device with the matching IP responds with its MAC address, enabling the sender to Map the IP Address to the correct MAC Address.

[ Option B ]

Given 4 network segments represented by points A1, B1, C1, and D1 interconnected in a mesh, we need to find the total number of mesh connections.

• In a full mesh network, every node is connected to every other node.
• The formula for the number of connections in a full mesh with n nodes is [n(n-1)/2].

With 4 nodes the number of connections is [4(4-1)/2] = [4*3/2] = 12/2 = 6.

[ Option A ]

In India, each person has only one Aadhaar Card, and each Aadhaar number belongs to only one person.

• Each person can possess only one unique Aadhaar Card.
• Each Aadhaar Card corresponds to exactly one person.

This is a One-to-One (1:1) relationship in the ER Model.

[ Option A ]

In networking, multiple access protocols are used to manage how devices share the same communication medium.
In wired networks (Ethernet), devices can easily detect collisions, so CSMA/CD is used. But in wireless networks, devices cannot detect collisions properly because they cannot listen while transmitting. Therefore, CSMA/CA is used in Wi-Fi, and it is not suitable for wired networks.

• CSMA/CD (Carrier Sense Multiple Access with Collision Detection), for wired networks.
• CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), for wireless networks.

[ Option A ]

The Total Length field in an IPv4 datagram header is 16 bits long. This field specifies the complete size of the IP packet, which includes both the header and the data portion.
Because it is a 16-bit field, it can represent values ranging from a minimum of 20 bytes (when no payload) up to a maximum of 65535 bytes.
 

[ Option B ]

ARIES stands for Algorithms for Recovery and Isolation Exploiting Semantics. It is a robust and widely-used database recovery algorithm designed to ensure data integrity and consistency in the event of system failures or crashes.
ARIES is based on the Write-Ahead Logging (WAL) protocol, which guarantees that any changes to the database are first recorded in a log before being applied to the database itself.
The correct order of applying the three passes in the ARIES recovery algorithm is Analysis, Redo, Undo.

[ Option C ]

ALOHA is a Random-Access Protocol used in computer networks for sharing a common communication channel.
It allows multiple users or stations to send data whenever they want, but collisions can occur if two or more stations send data at the same time.
Throughput means the rate of successful data transmission over a communication channel.

• G = The total transmission attempts per slot.
• e^−G = The probability that no other station transmits in the same slot, i.e., no collision.

OTHER RANDOM-ACCESS PROTOCOLS:

[ Option A ]

Automatic Repeat reQuest (ARQ) is a network protocol used to achieve Reliability in data transmission. Its primary function is to ensure that data packets sent from a sender are correctly received by the receiver. If an error is detected in a transmitted packet or if an acknowledgement is not received within a specified timeout period, ARQ triggers the retransmission of that packet until it is correctly received and acknowledged.
This mechanism helps to maintain data integrity and overcome issues such as lost or corrupted packets in unreliable communication channels.

[ Option C ]

The statement (I) is true because, in B+ trees, to maintain balance and efficient use of space, the number of children for each internal (non-leaf) node must be at least half of the maximum allowed children, up to the maximum n.
The statement (II) is false because, a clustering index is based on the order in which data records are stored physically. The search key for the clustering index is the attribute(s) on which the file is ordered, which may or may not be the primary key.
The statement (III) is true because, secondary indices typically maintain an index record for every tuple in the data file to provide quick access regardless of the clustering. Hence, secondary indices are dense meaning an index entry exists for every search-key value.
The statement (IV) is false because, by definition, a Dense Index has an index record for every search-key value in the data file. A Sparse Index has entries for only some search-key values.

[ Option D ]

TCP (Transmission Control Protocol) is a connection-oriented protocol, which means it establishes a reliable connection before sending data. The three-way handshake involves three steps, SYN, SYN-ACK, and ACK.

• SYN: Client sends a synchronize (SYN) packet to the server.
• SYN-ACK: Server responds with SYN + acknowledgment (ACK).
• ACK: Client sends back an ACK to the server.

After these three steps, the connection is established and both sides have agreed on initial sequence numbers.

[ Option A ]

In CIDR (Classless Inter-Domain Routing) notation, the suffix “/24” denotes that 24 bits are used for the network part of the IP address. This means that the first 24 bits out of the total 32 bits in an IPv4 address identify the network, while the remaining 8 bits are used for host addresses within that network.
The "/24" notation corresponds to a subnet mask of 255.255.255.0 in traditional dotted decimal format. It essentially tells how many bits are fixed for the network prefix, allowing flexible subnetting and efficient allocation of IP address space.

[ Option C ]

Stop-and-Wait ARQ is a protocol in which the sender transmits one data packet and waits for an acknowledgement before sending the next packet. Each data packet requires exactly one acknowledgement to confirm its successful receipt. Hence, if 10 data packets are sent, the receiver must send 10 acknowledgements.

[ Option B ]

To find which operations give the same output, we first identify the common tuples in both relations. The only matching rows between Student and Faculty are Cyber (300) and CIVIL (2000). This means the intersection Student ∩ Faculty contains exactly these two tuples.

Now, expression (B) calculates (Student ∩ Faculty) ∪ (Faculty ∩ Student). Since both intersections are the same, their union also gives the same two tuples: Cyber (300) and CIVIL (2000). Expression (D) directly performs Student ∩ Faculty, which naturally results in the same pair of tuples. Hence, B and D produce identical outputs.

[ Option A ]

Zeroconf (Zero Configuration) and Plug-and-Play mean that a device should automatically get network settings without manual configuration. The protocol that helps devices automatically get an IP address, subnet mask, and other settings is DHCP (Dynamic Host Configuration Protocol).

• It assigns IP addresses automatically.
• No manual setup is needed.

[ Option B ]

The OSI (Open Systems Interconnection) model has seven layers, with the Physical Layer at the bottom (Layer 1).
The physical layer main job is to send raw bits (0s and 1s) from one device to another through a physical medium like cables, radio waves, or fiber optics. It does not understand data, packets, or addresses, it only deals with electrical signals, light signals, or radio signals.

[ Option B ]

To create subnets in a Class B network, we start with the default subnet mask 255.255.0.0. The organization wants 64 departments, which means they need 64 subnets. To find how many bits are needed for subnetting, we check powers of two, i.e., 2ⁿ ≥ 64.
When we try 2⁶, we get 64, which matches the requirement. This means the network must borrow 6 bits from the host portion to create the subnets.
In a Class B address, the subnetting begins in the third octet. When we borrow 6 bits, the first 6 bits of the third octet become 1s. In binary, these 6 ones followed by two zeros give the value 252.
255.255.11111100.00000000

So, the subnet mask becomes, 255.255.252.0

[ Option A ]

The decomposition of schema R(A,B,C,D) with functional dependencies A→B and C→D into R1(AB) and R2(CD), is dependency preserving but not lossless join.
Lossless Join: A decomposition is lossless if you can always recover the original relation by joining the decomposed relations, without losing any data. For a lossless join, the intersection of the schemas must be a key in at least one of the decomposed relations.
Dependency Preserving: A decomposition is dependency preserving if every functional dependency in the original relation is still enforceable in at least one of the decomposed relations without needing to join.

• The intersection between R1 and R2 is empty (AB∩CD=∅), so the lossless join condition fails.
• The dependencies A→B and C→D can still be enforced within R1 and R2 respectively. So, these dependencies are preserved.

[ Option C ]

An organized collection of logically related data is called a Database. A database is designed to efficiently store, manage, and retrieve large amounts of data.

• Data is stored in a structured way.
• Different pieces of data are connected or related to each other.
• It helps in easy storage, searching, and management of information.

A Student database stores data like name, roll number, class, fees, marks, percentage, all related to Students.

[ Option D ]

A Join is a relational database operation that combines rows from two tables based on a related attribute. It helps in retrieving connected information stored across multiple tables. 
Among different types of joins, the Natural Join is a special type that automatically matches rows based on all columns with the same name and then merges them, removing duplicate columns in the output.

In this question, the natural join between R1 and R2 is performed on the common attributes Q and R. First, we identify matching pairs. In R1, the pairs (q, r) appear twice, and in R2, the same pair appears in three different rows. Each matching pair from R1 combines with all matching rows in R2, giving 2×3=6 tuples. 
Additionally, the pair (e, f) in R1 matches one row in R2, giving 1 more tuple. The other pair (i, j) has no match, so it contributes zero. Adding them together, the Natural Join produces 6+1+0 = 7 tuples.
 

[ Option C ]

The operation that requires two relations as input and needs these two relations to have a common attribute to form a new relation is the Natural Join operation.
Natural join automatically joins two relations based on all attributes with the same name and compatible data types in both relations. It matches and combines rows where the common attribute values are equal.

Relation Student:

Relation Marks:

Natural Join (Student ⋈ Marks) : The join matches rows where RollNo is common.

[ Option B ]

To determine the highest normal form of the relation S(S1,S2,S3,E1,E2) with the given functional dependencies:
FD1: S1→{S2,S3}
FD2: {E1,S3,S2}→S1
FD3: E2→{S3,S2,E1}
First of all, find the key. Using the above functional dependencies the E2 determine all the attributes, so, E2 is candidate key. That makes E2 the only prime attribute.
Prime Attribute : E2.
Non-Prime Attribute : S1, S2, S3, E1.

Check 2NF:
The relation is at least in 2NF, if key contains only one attribute, then there is no partial dependency because one attribute has no subset. So, the relation is in 2NF.

• If the proper subset of candidate key determines non-prime attribute, it is called Partial Dependency.

Check 3NF:
The relation is called in 3NF it is already exists in 2NF and there is no transitive dependency exists.

• If non-prime attribute can determine another non-prime attribute, then it is called Transitive Dependency.

In the given relation FD set, the S1 can determine S2 and S3. The S1, S2 and S3 are non-prime attributes so these violets the rule of transitive dependency.
So, the highest normal form the relation satisfies is Second Normal Form (2NF).

[ Option D ]

ICMP (Internet Control Message Protocol) is a network layer (Layer 3) protocol in the OSI model. It is used for sending error messages and network status information. For example, commands like ping and traceroute use ICMP to check if a device is reachable.

[ Option A ]

The Data Link Layer is responsible for Node-To-Node Delivery and ensures reliable communication over a physical link. It performs key functions such as Framing, Error Control, and MAC Addressing, all of which are essential for organizing data into frames, detecting, or correcting errors, and identifying devices on the network.

However, Congestion Control is typically not a function of the data link layer; it is primarily handled by higher layers such as the network or transport layer to manage traffic load and avoid network congestion.

[ Option B ]

Accessing a disk block involves three main components:
Seek Time: The time taken for the disk arm to move the read/write head to the track where the desired block is located.
Rotational Delay (Latency): The time it takes for the disk platter to rotate so that the desired sector is under the read/write head.
Transfer Time: The time required to actually read or write the data once the head is in position.
All three components combined give the total time required to access a disk block.
Total Access Time = Seek Time + Rotational Delay + Transfer Time

[ Option B ]

In the Relational Model, every attribute in a table must store a single, indivisible value. This means the model does not allow composite attributes, which can be divided into sub-parts, or multivalued attributes, which can hold more than one value at the same time. The type of rule that enforces this requirement is known as a Domain Constraint.

Domain constraints define what type of values an attribute (column) can store. They ensure that:

• Each attribute stores atomic values.
• No column can store multiple values.
• No column can contain a structured or composite value.

Thus, domain constraints automatically prevent composite and multivalued attributes.

[ Option D ]

In an ER (Entity–Relationship) Model, an attribute is a property or characteristic of an entity. It tells us something about the entity. Attributes describe the entity with the help of values.
For example, for entity Employee the Name, Age, Salary, Skills and for entity Student the Roll No, Course, Address are attributes.

• Attributes help us store meaningful and organized information about each entity in the system.

Types of Attributes:

Because an employee can have multiple skills, and ER models represent such attributes as Multivalued Attributes.

[ Option A ]

In a relational database table, Cardinality refers to the total number of rows or records present in the table. It represents how many individual data entries the table holds.
The Degree refers to the total number of columns or attributes in the table, which describe the structure of each record.

[ Option C ]

A superkey is any set of attributes that can uniquely identify a tuple in a relation. If you have a relation with n attributes and one candidate key consisting of k attributes, the total number of super keys is 2^n−k.
Remember, this formula can only work with a relation has only one candidate key consisting of k attributes.
Given,
Relation: R(A, B, C)
Total Attributes (A,B,C) n = 3.
Candidate key B : k = 1
Total super keys: 2³⁻¹ = 2² = 4.

[ Option A ]

The data item Q initially = 500.
Schedule Step by Step:

• T1: Read(Q) : Reads Value 500
• T2: Read(Q) : Also Reads Value 500
• T1: Q = Q + 100 : T1 computes 600 (Local T1 Value)
• T2: Q = Q + 100 : T2 computes 600 (Based on old Value 500 and Local T2 Value)
• T2: Write(Q) : T2 writes 600 to the database.
• T1: Write(Q) : T1 then writes 600 to the database, which overwrites T1 write.

Because both transactions read the original value 500 and each computed 600, the second write simply overwrites the first with the same value. The final value of Q after the last operation is 600.

[ Option C ]

SMTP (Simple Mail Transfer Protocol) is used to send email from one computer (Mail Server) to another over the internet. Whenever you send an email, SMTP is responsible for transferring your message from the sender’s server to the receiver’s server.
The SMTP operates over TCP, commonly on port 25, ensuring reliable delivery of messages across networks.

[ Option A ]

In SQL, the operation used to define automatic actions that the database system should perform when specific events occur (such as INSERT, UPDATE, or DELETE) is called Trigger. A trigger is a stored program that executes automatically whenever a specified event happens on a table.
Triggers help in maintaining data integrity, enforcing business rules, automating tasks like auditing changes, and validating data before or after modification. They run without explicit invocation by users, ensuring consistent and automatic enforcement of rules defined at the database level.

[ Option D ]

To find the network address of the subnet where:
IP address 172.16.123.213 
Subnet Mask 255.255.255.240
First, convert the subnet mask to binary 255.255.255.240 corresponds to: 11111111.11111111.11111111.11110000
The last octet’s binary mask is 11110000, meaning the subnet block size is 256−240=16.

Find the subnet block where 213 belongs:

213 falls in 208–223, so, network address is 172.16.123.208

Another alternative solution to find the network address for IP 172.16.123.213 with subnet mask 255.255.255.240 is to perform a bitwise AND operation between the IP address and the subnet mask.
IP: 172.16.123.213, last octet binary : 213=11010101
Subnet Mask: 255.255.255.240 last octet binary 240=11110000
Perform bitwise AND between IP and subnet mask
IP :                  1 1 0 1 0 1 0 1
Mask:             1 1 1 1 0 0 0 0
Bitwise AND: 1 1 0 1 0 0 0 0
Decimal of binary 11010000 is 208. So, combine with first three octets 172.16.123. Finally the network address is 172.16.123.208

[ Option B ]

In a database, a View is a relation that does not actually exist as a stored table in the logical model. Instead, it is created using a query and shown to the user as a Virtual Table. The data in a view comes from one or more real tables, but the view itself does not store data permanently.
To create a view, we use the CREATE VIEW command followed by the view name and a SELECT query that determines the view's contents.
CREATE VIEW view_name AS
SELECT column1, column2
FROM table_name
WHERE condition;

[ Option C ]

An ER (Entity-Relationship) Model is used to visually represent the structure of a database.

• It shows entities, attributes, and relationships.
• It focuses on what data is stored and how it is related, without worrying about how it is physically stored.

This type of representation corresponds to the Conceptual Schema of a database.

[ Option B ]

A MAC (Media Access Control) address is a hardware identifier assigned to each Network Interface Card (NIC). It works at the Data Link Layer of the OSI model and ensures that each device on a local network can be uniquely identified.

• MAC addresses are used to send data between devices on the same network segment.
• They are permanent and unique, unlike IP addresses which can change.
• A MAC address is 48 bits long.
• It is typically written in hexadecimal notation as six groups of two digits as 00:1B:2C:3E:4B:BB.
• The first 24 bits represent the manufacturer OUI (Organizationally Unique Identifier), and the last 24 bits represent the unique Device ID.

[ Option D ]

A Class B network has a default subnet mask of 255.255.0.0, meaning the first two octets (16 bits) represent the network portion. The given subnet mask is 255.255.248.0. To interpret this:

• The third octet, 248 in decimal, corresponds to the binary pattern 11111000. This indicates that 5 bits in the third octet are used for subnetting.
• Therefore, including the default 16 network bits of Class B, a total of 21 bits (16 + 5) are used as network bits in this subnet.
• The remaining 11 bits (32-21) are allocated for host addresses.

The number of usable host addresses per subnet is calculated as 2¹¹−2, which equals 2046. 
We subtract 2 because one address is the Network Address and one is the Broadcast Address, which cannot be assigned to hosts.
 

[ Option D ]

The number of attributes or columns in a relation is known as the Degree of the relation. Sometimes it is also called Arity.

[ Option D ]

DNS (Domain Name System) works like the “PHONEBOOK OF THE INTERNET”. It takes a human-readable domain name like www.surakuacademy.com and finds the corresponding numerical IP address (like 46.28.45.103) so that computers can locate and connect to the correct server. Without DNS, users would have to remember and type IP addresses instead of easy names.

What DNS Does:

• When you type a website name in the browser, DNS receives that name.
• It looks up its database (DNS servers) to find the correct IP address.
• It returns that IP address to your device.
• Your device then uses the IP address to connect to the correct web server.

[ Option C ]

A database system is designed to separate data from programs, so that if the data structure changes, programs do not need major rewriting. This feature is called Data Independence, and it is supported by the database approach.

[ Option C ]

Given, 
Message : 1001
CRC Polynomial (CRC Generator) : x³+x+1, binary 1011 (Degree 3)
Append 3 zero to the message because degree of polynomial is 3 or n-1 times (if n is CRC Generator).
Now perform Binary Division (Modulo 2):
Divide 1001000 by 1011 (Binary Division, XOR for Subtraction)
1001000 ÷ 1011, Remainder is 110.
This remainder is CRC bit.
Transmitted Message : Original Message + CRC Bits = 1001 + 110 = 1001110

[ Option C ]

NAV (Network Allocation Vector) is a virtual carrier sensing mechanism used in Wi-Fi (IEEE 802.11) networks as part of the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol.
It acts as a timer that indicates how long the wireless medium will be busy based on the duration information contained in MAC frame headers.

• It helps devices know how long the medium will be busy.
• This is part of CSMA/CA, which Wi-Fi uses to avoid collisions.
• Devices check NAV before sending data.

[ Option D ]

Reliable data transfer means ensuring that data reaches the receiver without errors, without loss, and in the correct order.
Reliable data transfer is implemented by the Transport Layer in the OSI model. The transport layer is responsible for providing end-to-end communication services for applications. 
It ensures reliable delivery of data through mechanisms such as error detection and correction, flow control, segmentation, acknowledgment of received data, and retransmission of lost or corrupted segments. 
Protocols like TCP (Transmission Control Protocol) at this layer offer connection-oriented and reliable communication by managing data packets and maintaining the order and integrity of the data transmitted between sender and receiver.

[ Option A ]

In IPv4, a packet may need to be fragmented if it is larger than the Maximum Transmission Unit (MTU) of the network.

Fragmentation: The large packet is broken into smaller fragments.
Reassembly: The receiver combines the fragments back into the original packet.
IPv4 uses two fields in the IP header to manage this process:

• More Fragments (MF) Flag: Indicates if more fragments follow.
• Fragment Offset: Shows the position of the fragment in the original packet.

These fields allow the receiver to correctly reassemble all fragments in order.

[ Option D ]

A spanning tree of a graph is a tree that connects all the vertices without forming any cycle.
For a complete graph K_n ,where every vertex is connected to every other vertex, the number of possible spanning trees is given by Cayley’s formula, T_n=nⁿ⁻².
Here, n = 5 so, T₅=5⁵⁻² = 5³ = 125.

[ Option C ]

In a slotted LAN, all n stations get a chance to send data in every time slot. Each station tries to send with a probability p. To find the probability that only one station sends data, we think about two things:

• One station must send, this happens with probability p.
• All the other (n – 1) stations must stay silent, each stays silent with probability 1-p, so together it becomes (1−p)ⁿ⁻¹.

Because any one of the n stations could be the one that transmits successfully, we multiply by n. So, the probability that only one station transmits is n×p×(1−p)ⁿ⁻¹.

[ Option C ]

In SQL (Structured Query Language), a view is a virtual table that is created based on the result of a query. It does not store data physically.
To create a view, we use the CREATE VIEW command followed by the view name and a SELECT query that determines the view's contents.
CREATE VIEW view_name AS
SELECT column1, column2
FROM table_name
WHERE condition;

[ Option D ]

The Data Manipulation Language (DML) is the part of SQL used to query and update data in a database.