An electrical circuit has only two states: ON and OFF. The binary number system has only two values corresponding to these states that represent high and low voltage levels, “1” (5 V) and “0” (0 V). These values are simply called as binary digits (bit, denoted by ‘b’) in computer systems. In computing, other than binary, octal and hexadecimal number systems are also used as more compact forms for representing binary numbers. In computer systems, a byte (denoted by ‘B’) is a unit of data that consists of 8 bits. It is used to represent a character. A nibble is half byte. A word is a standard memory bus width in computer architecture. It can have a length of 16 bits, 32 bits, 64 bits etc. The correct option is A.