Basic Computer: Number Systems & Codes MCQ - Practice Questions with Answers

Binary is a base-2 number system, so each place represents a power of 2. For 1011, read from right to left: 1 × 2^0 = 1, 1 × 2^1 = 2, 0 × 2^2 = 0, and 1 × 2^3 = 8. Adding these place values gives 8 + 0 + 2 + 1 = 11. The cue in the question is the word "binary", so the digits must be evaluated with powers of 2, not powers of 10.

BCD means Binary Coded Decimal. Its key idea is not to convert the whole decimal number into one binary value. Instead, each decimal digit is converted separately into its 4-bit binary form. In the stem, 5 becomes 0101 and 9 becomes 1001, so decimal 59 is written as 0101 1001 in BCD. This example proves the assertion and explains why BCD is different from pure binary conversion. Therefore both A and R are true, and R explains A.

In the binary system, place values are powers of 2 from right to left: 1, 2, 4, 8 and so on. To write decimal 13 in binary, split it into powers of 2: 13 = 8 + 4 + 1. Therefore the bits for 8, 4 and 1 are set to 1, while the bit for 2 is 0. Reading the four bits in order gives 1101. This matches option A.

ASCII stands for a widely used character encoding scheme in basic computer studies. It assigns numeric codes to characters such as English letters, digits, punctuation marks and control characters, so Statement 1 is correct. Standard ASCII is historically a 7-bit code, giving 128 possible code values. Extended versions later used 8 bits, but the question says standard ASCII originally, which points to 7 bits. Therefore both statements are correct, and option C is the defensible answer.

The cue in the question is the hexadecimal number system. Hexadecimal means base 16. Since ordinary digits provide only ten symbols, hexadecimal uses 0 to 9 for the first ten values and A to F for values 10 to 15. This is why one hexadecimal digit can represent four binary bits. Options B, C and D describe octal, binary and decimal systems respectively, so option A is the correct statement.