Q.1 Which number system uses only two digits, 0 and 1?
Decimal
Binary
Octal
Hexadecimal
Explanation - Binary is a base-2 number system that uses only 0 and 1 to represent numbers.
Correct answer is: Binary
Q.2 What is the decimal equivalent of binary number 1011?
11
13
9
15
Explanation - Binary 1011 = 1*2^3 + 0*2^2 + 1*2^1 + 1*2^0 = 8 + 0 + 2 + 1 = 11.
Correct answer is: 11
Q.3 The hexadecimal number '1A' is equal to what decimal number?
26
28
30
24
Explanation - Hex 1A = 1*16 + 10 = 26 in decimal.
Correct answer is: 26
Q.4 Which of the following is an octal number?
128
75
1F
1010
Explanation - Octal numbers use digits 0 to 7 only. '75' is valid octal.
Correct answer is: 75
Q.5 What is the binary equivalent of decimal 25?
11001
10101
11100
10011
Explanation - Decimal 25 = 16 + 8 + 0 + 0 + 1 = 11001 in binary.
Correct answer is: 11001
Q.6 In which number system is 'F' a valid digit?
Binary
Decimal
Hexadecimal
Octal
Explanation - 'F' represents 15 in hexadecimal (base 16).
Correct answer is: Hexadecimal
Q.7 The decimal number 50 is represented as what in octal?
62
64
52
46
Explanation - Decimal 50 ÷ 8 = 6 remainder 2 → octal = 62.
Correct answer is: 62
Q.8 What is the sum of binary numbers 1010 and 1101?
10111
11101
10101
10011
Explanation - 1010 + 1101 in binary = 10111.
Correct answer is: 10111
Q.9 Which of the following is not a valid binary number?
11001
10201
1010
1111
Explanation - Binary numbers can only have 0 and 1. '10201' has 2, so it is invalid.
Correct answer is: 10201
Q.10 The 2's complement of binary number 1010 is:
0110
0101
1110
1011
Explanation - 2's complement: invert digits (1010 → 0101) and add 1 → 0101 + 1 = 0110.
Correct answer is: 0110
Q.11 Which number system is most commonly used in digital computers?
Decimal
Binary
Octal
Hexadecimal
Explanation - Computers use binary because digital circuits have two states: ON and OFF.
Correct answer is: Binary
Q.12 What is the decimal equivalent of octal number 77?
63
56
72
49
Explanation - Octal 77 = 7*8 + 7 = 56 + 7 = 63 decimal.
Correct answer is: 63
Q.13 What is the binary representation of hexadecimal 'C'?
1100
1010
1110
1001
Explanation - Hex C = decimal 12 → binary 1100.
Correct answer is: 1100
Q.14 Which is the correct sum of octal numbers 25 and 17?
44
42
36
40
Explanation - Octal 25 + 17 = 25(21 decimal) + 17(15 decimal) = 36 decimal → 44 octal.
Correct answer is: 44
Q.15 What is the decimal equivalent of binary 111111?
63
31
45
55
Explanation - Binary 111111 = 32+16+8+4+2+1 = 63.
Correct answer is: 63
Q.16 Which arithmetic operation is easiest to implement in binary systems?
Addition
Multiplication
Division
Subtraction
Explanation - Binary addition is straightforward in digital circuits using logic gates.
Correct answer is: Addition
Q.17 Convert decimal 255 to hexadecimal.
FF
FE
AA
F0
Explanation - 255 ÷ 16 = 15 remainder 15 → FF in hex.
Correct answer is: FF
Q.18 The decimal number 7 is represented as what in 3-bit binary?
111
011
101
110
Explanation - Decimal 7 = 4+2+1 → binary 111 using 3 bits.
Correct answer is: 111
Q.19 Which number system uses base 8?
Binary
Decimal
Octal
Hexadecimal
Explanation - Octal is a base-8 system using digits 0-7.
Correct answer is: Octal
Q.20 What is the 1's complement of binary number 10101?
01010
10101
01101
10010
Explanation - 1's complement is obtained by inverting all bits: 10101 → 01010.
Correct answer is: 01010
Q.21 Which of the following is a valid hexadecimal number?
2G
3F
89
1012
Explanation - Hexadecimal digits are 0-9 and A-F. '3F' is valid.
Correct answer is: 3F
Q.22 Binary 1001 multiplied by 10 equals:
10010
10011
10100
11001
Explanation - Binary multiplication by 10 (decimal 2) is equivalent to a left shift: 1001 << 1 = 10010.
Correct answer is: 10010
Q.23 Decimal 1000 in binary is:
1111101000
1001110000
1111010000
1111101100
Explanation - 1000 decimal = 1111101000 in binary.
Correct answer is: 1111101000
Q.24 What is the decimal equivalent of hexadecimal '2F'?
47
32
35
43
Explanation - Hex 2F = 2*16 + 15 = 32 + 15 = 47 decimal.
Correct answer is: 47