Which statement correctly defines number bases and BCD?

• A. Binary is base-2, decimal is base-10, hexadecimal is base-16; BCD encodes each decimal digit with a fixed binary pattern.
• B. Binary is base-2, decimal base-10, hexadecimal base-16; BCD encodes the entire number as one binary string.
• C. BCD encodes groups of digits, not individual digits.
• D. BCD stands for Binary Coded Decimal and is unrelated to decimal digits.

Answer: (A)

Understanding number bases and how Binary-Coded Decimal works helps you see why that statement is correct. A base defines the set of digits you can use and how their positions stack to form numbers. Binary uses base-2 with digits 0 and 1, decimal uses base-10 with digits 0 through 9, and hexadecimal uses base-16 with digits 0–9 and A–F. Binary-Coded Decimal then takes each decimal digit and encodes it separately using a fixed binary pattern, typically 4 bits per digit. For example, the decimal number 42 becomes 0100 0010: the first digit 4 is encoded as 0100, the second digit 2 as 0010, and the two patterns are concatenated. This per-digit encoding is what makes BCD different from simply turning the whole number into a single binary string.

So the statement that correctly defines both the bases and what BCD does is the one that lists binary base-2, decimal base-10, hexadecimal base-16, and states that BCD encodes each decimal digit with a fixed binary pattern. The other ideas mischaracterize BCD: encoding the entire number as one binary string isn’t how BCD works, encoding groups of digits instead of individual digits isn’t accurate, and claiming BCD isn’t related to decimal digits is simply incorrect.