AmbifulWorksheets
Practice that never repeats
CBSE · Class 11 · Computer Science

Boolean Logic

Standard difficulty · 20 questions · 40 marks · Time: 36 minutes

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
Which gate gives an output of 1 only when all its inputs are 1?
  1. NAND
  2. XOR
  3. OR
  4. AND
2.
A two-input gate gives these outputs for the inputs 00, 01, 10 and 11: 0, 1, 1, 1. Which gate is it?
  1. XOR gate
  2. NOR gate
  3. OR gate
  4. NAND gate
3.
In the truth table of NOT C AND (B OR NOT A), in how many of the 8 rows is the output 1?
  1. 5
  2. 3
  3. 4
  4. 2
4.
By De Morgan's law, NOT (NOT X OR Y) is equal to:
  1. X OR NOT Y
  2. X OR Y
  3. X AND NOT Y
  4. NOT X AND Y
5.
For which of these inputs is R XOR (P OR Q) equal to 1?
  1. P = 0, Q = 1, R = 1
  2. P = 1, Q = 0, R = 1
  3. P = 1, Q = 1, R = 0
  4. P = 1, Q = 1, R = 1
6.
X and Y go into an XOR gate; its output and Z go into a NOR gate. Which expression gives the final output?
  1. NOT ((X XOR Y) OR Z)
  2. (X XOR Y) XOR Z
  3. X XOR NOT (Y OR Z)
  4. NOT (X AND Y) XOR Z
7.
X and Y go into a NOR gate; its output and Z go into a NAND gate. For how many of the 8 input combinations is the final output 1?
  1. 7
  2. 8
  3. 1
  4. 6
8.
A NAND gate has 3 inputs. In how many of the 8 rows of its truth table is the output 1?
  1. 1
  2. 8
  3. 3
  4. 7
Section B — Short answer8 × 2 = 16 marks
9.
State both of De Morgan’s laws.
10.
For A = 1 and B = 1, find (a) A NAND B (b) A OR B (c) A NOR B.
11.
Write the output column of the truth table of NOT (NOT N XOR (N OR NOT M)) for the rows MN = 00, 01, 10, 11.
12.
Use De Morgan's law to write NOT (X OR NOT Y) without a NOT in front of the brackets.
13.
In how many of the 8 rows of the truth table is (P XOR NOT Q) OR R equal to 1?
14.
A and B go into an AND gate; its output and C go into a NOR gate. What is the final output for (a) A = 0, B = 0, C = 1 (b) A = 1, B = 0, C = 0?
15.
Two-input gates give these outputs for the inputs 00, 01, 10, 11. Name each gate: (a) 0, 1, 1, 1 (b) 0, 1, 1, 0
16.
For A = 0 and B = 1, find (a) NOT (A AND B) (b) NOT A OR NOT B (c) NOT (A OR B) (d) NOT A AND NOT B.
Section C — Word problems4 × 4 = 16 marks
17.
Draw the symbols and write the truth tables of the AND, OR and NOT gates.
18.
Make the truth table of Y OR (X XOR Z). Write its output column for the rows XYZ = 000, 001, 010, 011, 100, 101, 110, 111.
19.
A and B go into an XOR gate; its output and C go into an OR gate. (a) Write the Boolean expression for the final output. (b) What is the output for A = 1, B = 1, C = 1? (c) For how many of the 8 input combinations is the output 1?
20.
(a) Prove the De Morgan's law NOT (P OR Q) = NOT P AND NOT Q with a truth table: write both output columns for PQ = 00, 01, 10, 11. (b) Use De Morgan's law to simplify NOT (NOT P AND Q).
AmbifulWorksheets
Practice that never repeats
CBSE · Class 11 · Computer Science

Answer key

Boolean Logic · AW-11CS-BLG-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) AND—
2(c) OR gateOR: 0, 1, 1, 1
3(b) 3output column: 1, 0, 1, 0, 0, 0, 1, 0
4(c) X AND NOT YNOT (P OR Q) = NOT P AND NOT Q, and NOT NOT P = P
5(c) P = 1, Q = 1, R = 0work out the expression for each row
6(a) NOT ((X XOR Y) OR Z)first gate: X XOR Y
7(a) 7output column: 1, 0, 1, 1, 1, 1, 1, 1
8(d) 7NAND is every row but one
9NOT (A AND B) = NOT A OR NOT B; NOT (A OR B) = NOT A AND NOT B.—
10(a) 0; (b) 1; (c) 0NAND: 1, 1, 1, 0; OR: 0, 1, 1, 1; NOR: 1, 0, 0, 0
111, 0, 0, 000 → 1; 01 → 0; 10 → 0; 11 → 0
12NOT (X OR NOT Y) = NOT X AND YNOT changes OR to AND and is applied to each part; NOT NOT P = P
136output column: 1, 1, 0, 1, 0, 1, 1, 1
14(a) 0; (b) 1output = NOT ((A AND B) OR C)
15(a) OR; (b) XOR—
16(a) 1; (b) 1; (c) 0; (d) 0(a) and (b) are always equal, and so are (c) and (d): De Morgan’s laws
17AND (D-shaped): 1 only for 11; OR (curved): 0 only for 00; NOT (triangle with a circle): 0 → 1, 1 → 0.—
180, 1, 1, 1, 1, 0, 1, 1000 → 0; 001 → 1; 010 → 1; 011 → 1; 100 → 1; 101 → 0; 110 → 1; 111 → 1
19(a) (A XOR B) OR C; (b) 1; (c) 6output column: 0, 1, 1, 1, 1, 1, 0, 1
20(a) 1, 0, 0, 0 and 1, 0, 0, 0: the columns are equal; (b) P OR NOT Q00 → 1; 01 → 0; 10 → 0; 11 → 0