O Level / IGCSE Computer Science chapter 10: Boolean logic MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
28 exam-style questions on Boolean logic, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A logic gate symbol is drawn as a triangle with a small circle at its output. Which gate is it?
A
AND
B
NOT
C
NOR
D
XOR
Show answer
Answer: B. The NOT gate symbol is a triangle with a small circle (the inversion bubble) at the output. It is the only gate with one input.
2. For X = A XOR (B AND C), what is X when A = 1, B = 1 and C = 1?
A
B AND C = 1 and 1 XOR 1 = 1, so X = 1
B
B AND C = 1 and 1 XOR 1 = 0, so X = 0
C
B AND C = 0 and 1 XOR 0 = 1, so X = 1
D
B AND C = 0 and 1 XOR 0 = 0, so X = 0
Show answer
Answer: B. B AND C = 1. Then A XOR 1 = 1 XOR 1 = 0, because XOR gives 0 when both inputs are the same.
3. Output X is 1 when at least two of the three inputs A, B and C are 1. In how many of the eight rows of the truth table is X = 1?
A
3
B
1
C
4
D
7
Show answer
Answer: C. Rows with at least two 1s are 011, 101, 110 and 111: four rows. Forgetting that 111 also has at least two 1s gives 3.
4. In a circuit, A goes through a NOT gate. NOT A and B go into an AND gate giving P. P and C go into a NOR gate giving X. Which input combination gives X = 1?
A
A = 0, B = 1, C = 0
B
A = 0, B = 0, C = 1
C
A = 1, B = 1, C = 1
D
A = 1, B = 0, C = 0
Show answer
Answer: D. NOR gives 1 only when P = 0 and C = 0. For 1,0,0: NOT A = 0, so P = 0, and C = 0, so X = 1. For 0,1,0, P = 1; the other two have C = 1.
5. A logic gate symbol has the curved shield shape of an OR gate, with an extra curved line drawn across its inputs and no circle at the output. Which gate is it?
A
NOR
B
XOR
C
NAND
D
NOT
Show answer
Answer: B. The extra curved line at the inputs marks the XOR (EOR) gate. A circle at the output of an OR shape would make it NOR.
6. A heater H is on (H = 1) when the room is cold (C = 1) and the window is closed (W = 0). Which row of the truth table has H = 1?
A
C = 0, W = 0
B
C = 0, W = 1
C
C = 1, W = 1
D
C = 1, W = 0
Show answer
Answer: D. The heater needs the room to be cold (C = 1) and the window closed (W = 0). This is H = C AND NOT W, true only for C = 1, W = 0.
7. In a circuit, input A passes through a NOT gate. Its output and input B go into an OR gate, whose output is X. Which expression matches the circuit?
A
X = NOT (A OR B)
B
X = NOT A OR B
C
X = A OR NOT B
D
X = NOT A AND B
Show answer
Answer: B. Only A is inverted before the OR gate, so X = NOT A OR B. NOT (A OR B) would invert the output of the OR gate instead.
8. A circuit is a single NAND gate with inputs A and B. For the rows A,B = 0,0 / 0,1 / 1,0 / 1,1, what is the output column?
A
0 / 0 / 0 / 1
B
1 / 1 / 1 / 0
C
1 / 0 / 0 / 0
D
0 / 1 / 1 / 0
Show answer
Answer: B. NAND is NOT AND. AND gives 0, 0, 0, 1, so NAND gives 1, 1, 1, 0. 1, 0, 0, 0 is NOR and 0, 1, 1, 0 is XOR.
9. A pump P switches on (P = 1) when the water level is low (L = 1) and the temperature is not below freezing. T = 1 means the temperature is below freezing. Which expression is correct?
A
P = L AND T
B
P = L OR NOT T
C
P = NOT L AND T
D
P = L AND NOT T
Show answer
Answer: D. The pump needs a low level (L = 1) and not freezing (T = 0, so NOT T = 1): P = L AND NOT T.
10. In the four-row truth table for X = NOT (A OR B), in how many rows is X = 1?
A
0
B
1
C
2
D
3
Show answer
Answer: B. A OR B is 0 only when A = 0 and B = 0, so NOT (A OR B) is 1 in that single row. This is the NOR function.
28, each with the answer and a short explanation, across 3 topics: Logic gates, Logic circuits and logic expressions, Truth tables. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Computer Science chapter 10 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
