NEB Grade XI Computer Science Set 1 (New Course) — Answer Key, Important Questions & Free PDF

Grade XI Computer Science under the New Course (Code 4271 ‘A’) is one of the shorter papers in the NEB suite — just 2 hours and 50 full marks, compared to the 3-hour, 75-mark papers for Physics, Chemistry, and Biology. But shorter doesn’t mean easier to score well on. The 50 marks are spread across three groups: 9 marks of objective MCQs, 25 marks of short-answer questions (including one C programming numerical and one HTML question), and 16 marks of long-answer questions that demand either a complete block diagram of computer architecture or a working C program for matrix addition, followed by a 8-mark question on logic gates requiring both gate symbols and truth tables.

What’s distinctive about this Set 1 paper is that it covers a deliberately wide spread of the Computer Science syllabus in just 16 questions — computer hardware (CPU, memory types), digital logic (AND, OR, NAND, XOR gates), system software, word processing shortcuts, programming (nested loops in C, factorial program, matrix addition), web technology (HTML tags and list types), multimedia, and cybersecurity. A student who’s prepared deep in one area but neglected others will feel this breadth acutely. In particular, the C programming questions (Q13 and Q15 OR) are where many students lose the most marks, not because the programs are complex, but because small syntax errors (missing semicolons, wrong data type declarations, incorrect loop logic) in handwritten code can easily cost 2-3 marks on a 5-mark or 8-mark answer.

Below, you’ll find the complete MCQ answer key with explanations, a breakdown of all topics covered, a curated list of important questions and program types for your final exam, FAQs with fully worked answers (including complete C programs and truth table explanations), and the complete downloadable question paper. Whether you’re brushing up on logic gates, practicing C programs on paper, or making sure you know the HTML tags that NEB consistently tests, this guide should cover what you need.

Quick Navigation

• Download Full Question Paper (PDF)
• MCQ Answer Key
• Topics Covered in This Paper
• Important Questions and Programs for Your Final Exam
• FAQs with Complete Answers and C Programs
• How to Use This Paper Effectively

View the Full Question Paper

Get the complete NEB Grade XI Computer Science Set 1 (New Course) paper as a PDF.

MCQ Answer Key — NEB Computer Science Grade XI, Set 1

All 9 MCQs from Group A, 1 mark each (9×1=9 marks).

Quick explanations: Q1 — The CPU contains three main components: the ALU (Arithmetic Logic Unit, which performs calculations and logical operations), the CU (Control Unit, which manages instruction execution), and registers/cache. Monitor, modem, and printer are all peripheral devices, not CPU components. Q2 — PROM (Programmable Read-Only Memory) can be programmed exactly once (by the manufacturer or user using a special device), after which it becomes permanent and cannot be erased — making it “non-volatile and written only once.” EPROM can be erased using UV light; EEPROM can be erased electrically; RAM is volatile. Q3 — An AND gate produces a HIGH output (1) only when ALL inputs are HIGH (1). If any input is 0, the output is 0 — this is the fundamental AND logic. Q4 — System software includes operating systems (e.g., Windows, Linux), compilers (which translate high-level code to machine code), and utility programs (like antivirus, disk cleanup) — all of the above are system software. Q9 — Note: the paper uses “Passive attracts” which appears to be a typo for “Passive attacks.” Passive attacks (such as eavesdropping and traffic analysis) ARE actually classified as security threats. Among the listed options, the closest “not a security threat” might be a printing error issue in the original paper — interruption, modification, and interception are all standard security threats. Passive attacks (correctly spelled) are also threats, making this question ambiguous. Verify against your official answer key.

Topics Covered in This Paper

• Computer Hardware and Organization (Q1, Q15): CPU components (ALU, CU, registers), computer architecture block diagram, input/output units, memory unit, bus systems.
• Memory Types (Q2, Q10): volatile vs. non-volatile memory, PROM, EPROM, EEPROM, RAM, ROM; primary memory vs. secondary memory — definitions and differences.
• Number Systems and Binary Arithmetic (Q10 OR): binary subtraction using 1’s complement and 2’s complement methods.
• Digital Logic and Boolean Algebra (Q3, Q16): AND, OR, NAND, XOR gates — definitions, gate symbols, truth tables, and behavior.
• System Software (Q4, Q11): types of software — system software (OS, compiler/interpreter, utilities) vs. application software.
• Word Processing Shortcuts (Q5): common keyboard shortcuts (Ctrl+B = Bold, Ctrl+C = Copy, Ctrl+V = Paste, Ctrl+F = Find, etc.).
• Programming Concepts in C (Q6, Q13, Q15 OR): nested loops, factorial program, matrix addition program.
• Web Technology and HTML (Q7, Q12): HTML tags (paragraph tag), types of HTML lists (ordered, unordered, definition list).
• Multimedia (Q8, Q12 OR): definition of multimedia, applications of multimedia.
• Cybersecurity (Q9, Q14): security threats vs. non-threats, types of cybercrime, prevention methods.

Important Questions and Programs for Your Final Exam

These topics from Set 1 consistently reappear in NEB Computer Science papers. For the C programs especially, practice writing them by hand — syntax errors in handwritten code are the single biggest source of lost marks in this section.

• CPU components — ALU, CU, and registers with their specific roles
• Types of memory — ROM subtypes (PROM, EPROM, EEPROM), RAM, primary vs. secondary memory
• Binary subtraction using 1’s complement and 2’s complement — step-by-step method
• AND, OR, NOT, NAND, NOR, XOR, XNOR gates — gate symbols, truth tables, and Boolean expressions
• Computer architecture block diagram — labeled diagram with explanations of each component
• Types of computer software — system software vs. application software with examples
• Common keyboard shortcuts in MS Word/Excel (Ctrl+B, Ctrl+C, Ctrl+V, Ctrl+F, Ctrl+Z, etc.)
• Nested loops in C — syntax and typical use cases
• C program to find the factorial of a given number
• C program for matrix addition (two 3×3 matrices)
• HTML list types — ordered list (ol), unordered list (ul), definition list (dl) with tags and syntax
• Multimedia — definition, components (text, audio, video, image, animation), and applications
• Types of cybercrime (hacking, phishing, identity theft, cyberbullying, virus attacks)
• Cybercrime prevention methods (strong passwords, firewalls, antivirus, encryption, safe browsing)

Frequently Asked Questions

What’s the difference between PROM, EPROM, and EEPROM (Q2)?

All three are types of non-volatile ROM that retain data without power, but they differ in how (or whether) they can be reprogrammed. PROM (Programmable ROM) is blank when manufactured and can be programmed exactly once using a special device (a “PROM burner”) — after that, the programming is permanent and irreversible. EPROM (Erasable PROM) can be erased by exposing the chip to ultraviolet (UV) light through a quartz window on the chip’s package, then reprogrammed; this erasure-and-reprogram cycle can be repeated many times. EEPROM (Electrically Erasable PROM) can be erased and reprogrammed using electrical signals alone, without removing the chip from the circuit — making it the most flexible of the three, and the technology behind modern flash memory (USB drives, SSDs, etc.).

How do you subtract (1000)₂ from (1010)₂ using 1’s and 2’s complement (Q10 OR)?

We need to calculate 1010 − 1000 (which equals 0010 = 2 in decimal, as a quick check).

Using 1’s complement method: Step 1 — Find the 1’s complement of 1000 (the subtrahend): flip all bits → 0111. Step 2 — Add this to the minuend 1010: 1010 + 0111 = 10001 (5-bit result). Step 3 — An end-around carry occurs (the 5th bit is 1), so add this carry back to the result: 0001 + 1 = 0010. Result: 0010 = 2 in decimal. ✓

Using 2’s complement method: Step 1 — Find the 2’s complement of 1000: first find 1’s complement (0111), then add 1 → 0111 + 1 = 1000. (Note: the 2’s complement of 1000 is 1000, since it represents −8 in signed binary — but for this subtraction, it works as follows.) Step 2 — Add to the minuend 1010: 1010 + 1000 = 10010 (5-bit result). Step 3 — Discard the carry (the 5th bit): result is 0010. Result: 0010 = 2 in decimal. ✓

How do you explain AND, OR, NAND, and XOR gates with truth tables (Q16)?

Each logic gate performs a specific Boolean operation on its input(s). Here are all four with their truth tables:

AND Gate — Output is HIGH (1) only when ALL inputs are HIGH. Boolean expression: Y = A · B (or A AND B)

OR Gate — Output is HIGH (1) when AT LEAST ONE input is HIGH. Boolean expression: Y = A + B (or A OR B)

NAND Gate — Output is LOW (0) only when ALL inputs are HIGH; otherwise HIGH. It is the complement (NOT) of AND. Boolean expression: Y = ¬(A · B) or Y = (A · B)’

XOR Gate (Exclusive OR) — Output is HIGH (1) when inputs are DIFFERENT (one high, one low); output is LOW when inputs are the SAME. Boolean expression: Y = A ⊕ B

What is the difference between primary and secondary memory (Q10)?

Primary memory (also called main memory) is directly accessible by the CPU, operates at high speed, and is used to store data and instructions that the CPU is currently processing. It is typically volatile (data is lost when power is off) — RAM is the main example — though ROM (which stores firmware/BIOS) is an exception. Primary memory has limited capacity and higher cost per unit of storage. Secondary memory (also called auxiliary or storage memory) is not directly accessible by the CPU (data must first be loaded into primary memory), operates at much slower speeds than primary memory, and is typically non-volatile (data persists without power). Examples include hard disk drives (HDDs), solid-state drives (SSDs), USB flash drives, optical discs, and magnetic tapes. Secondary memory has much larger capacity and lower cost per unit than primary memory, making it suitable for long-term data storage.

What are the three types of lists in HTML (Q12)?

HTML supports three main list types: an ordered list uses the <ol> tag, and list items (<li>) within it are automatically numbered (1, 2, 3… or A, B, C… or i, ii, iii…) — used when the sequence of items matters, such as step-by-step instructions. An unordered list uses the <ul> tag, and list items (<li>) are displayed with bullet points (•, ○, ■, etc.) — used when the order of items doesn’t matter, such as a list of features. A definition list uses the <dl> tag, containing pairs of <dt> (definition term) and <dd> (definition description) elements — used for glossaries or any list of terms with their explanations. Example:

<ol><li>First item</li><li>Second item</li></ol> — produces a numbered list. <ul><li>Bullet item</li><li>Another item</li></ul> — produces a bulleted list. <dl><dt>HTML</dt><dd>HyperText Markup Language</dd></dl> — produces a term-description pair.

What are the main prevention methods for cybercrime (Q14)?

Cybercrime prevention involves both technical and behavioral measures: using strong, unique passwords and changing them regularly (and enabling two-factor authentication where available) reduces unauthorized access to accounts; installing and keeping updated antivirus and anti-malware software protects against virus attacks, ransomware, and spyware; using a firewall (hardware or software) monitors and filters incoming and outgoing network traffic, blocking suspicious connections; keeping operating systems and software updated patches security vulnerabilities that attackers commonly exploit; practicing safe browsing habits (not clicking suspicious links, not downloading files from untrusted sources, verifying website authenticity before entering personal information) prevents phishing and drive-by download attacks; encrypting sensitive data ensures that even if data is intercepted, it cannot be read without the decryption key; and regular data backups minimize the damage from ransomware attacks or data loss incidents by allowing recovery of important files without paying ransoms or losing work.

Complete C program to find the factorial of a number (Q13):

Here is a complete, exam-ready C program. When writing this by hand in the exam, pay special attention to the semicolons at the end of every statement, the correct use of long data type (since factorials grow large quickly), and the loop structure.

#include <stdio.h>

int main() {
    int n, i;
    long fact = 1;

    printf("Enter a number: ");
    scanf("%d", &n);

    if (n < 0) {
        printf("Factorial is not defined for negative numbers.\n");
    } else {
        for (i = 1; i <= n; i++) {
            fact = fact * i;
        }
        printf("Factorial of %d = %ld\n", n, fact);
    }

    return 0;
}

Key points to remember: declare fact as long (not int) to handle larger factorials without overflow; the loop runs from 1 to n (inclusive); the negative number check is good practice and may earn extra marks for completeness; use %ld format specifier for long type.

Complete C program for 3×3 matrix addition (Q15 OR):

This is a standard nested-loop matrix problem. The outer two loops are for reading the two matrices, and the innermost operation is the element-wise addition.

#include <stdio.h>

int main() {
    int a[3][3], b[3][3], c[3][3];
    int i, j;

    printf("Enter elements of first 3x3 matrix:\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("a[%d][%d]: ", i, j);
            scanf("%d", &a[i][j]);
        }
    }

    printf("Enter elements of second 3x3 matrix:\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("b[%d][%d]: ", i, j);
            scanf("%d", &b[i][j]);
        }
    }

    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            c[i][j] = a[i][j] + b[i][j];
        }
    }

    printf("Result matrix (A + B):\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("%d ", c[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Key points: three 3×3 integer arrays (a, b, c); two nested loops for input (repeated twice, once per matrix); one nested loop for addition; one nested loop for output with a newline after each row (printf("\n") inside the outer loop, outside the inner loop).

What is computer architecture and what are its main components (Q15)?

Computer architecture refers to the design and organization of a computer system’s fundamental components and how they interact to execute instructions and process data. The main components are: the CPU (Central Processing Unit), which consists of the ALU (performs arithmetic and logical operations), the CU (Control Unit, which fetches, decodes, and executes instructions), and registers (small, fast temporary storage within the CPU); the Memory Unit, which includes primary memory (RAM for working storage, ROM for firmware) and cache memory (fast buffer between CPU and RAM); the Input Unit, which includes devices that take data into the computer (keyboard, mouse, scanner, microphone); the Output Unit, which includes devices that present results to the user (monitor, printer, speakers); and the Bus System, which consists of parallel communication pathways — the Data Bus (carries data between components), the Address Bus (carries memory addresses), and the Control Bus (carries control signals). All components communicate through the system bus, with the CPU orchestrating operations by fetching instructions from memory, decoding them, and directing the ALU to execute them.

How to Use This Paper Effectively

The two-hour time limit is tighter than most NEB papers — 9 MCQs, 5 short-answer questions (including a C program), and 2 long-answer questions (one of which requires a block diagram and another a full C program) in 120 minutes leaves very little margin for confusion or second-guessing. In practice: budget about 10 minutes for MCQs, 50 minutes for Group B (10 minutes per question), and 55 minutes for Group C (25-30 minutes each), keeping 5 minutes at the end for a quick review.

The C programming questions (Q13, Q15 OR) reward students who’ve practiced writing complete programs by hand — not just knowing the algorithm but being able to write syntactically correct C without an IDE to catch errors. In the week before your exam, write the factorial program and the matrix addition program from memory at least three times each, without looking at notes. A program that compiles and runs correctly in your head is a program you can write cleanly in the exam.

Logic gates (Q16) and computer architecture (Q15) are the two most structured answers in this paper, and both reward the same approach: start with a clear definition, draw the diagram (gate symbol or architecture block diagram) first and label it carefully, then build your written explanation around the diagram. Examiners mark diagrams and truth tables separately from prose explanations, so even a partially incomplete written explanation accompanied by a correct, complete diagram and truth table can still score well.