Correct Option: D

BCD code (Binary coded decimal) code is also known as 8 – 4 – 2 – 1 code. This is because 8, 4, 2 and 1 are the weights of the four bits of the BCD code. The weight of the LSB is 2⁰ or 1, that of the next higher order bit is 2¹ or 2, that of the next higher order bit is 2² or 4, and that of the MSB is 2³ or 8. Therefore, this is a weighted code and arithmetic operations can be per for med using this code, which will be discussed later on. The bit assignment 0101, for example, can be interpreted by the weights to represent the decimal digit 5 because 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 5. Since four binary bits are used the maximum decimal equivalent that may be coded is 15₁₀ (i.e., 1111₂). But the maximum decimal digit available is 9₁₀. Hence the binary codes 1010, 1011, 1100, 1101, 1110, 1111, representing 10, 11, 12, 13, 14, and 15 in decimal are never being used in BCD code. So these six codes are called forbidden codes and the group of these codes is called the forbidden group in BCD code. BCD code for decimal digits 0 to 9 is shown in the following table.