Explanation: the code where all successive numbers differ from their preceding number by single bit is gray code. it is an unweighted code. the most important characteristic of this code is that only a single bit change occurs when going from one code number to next. bcd code is one in which decimal digits are represented by a group of 4-bits each, whereas, in excess-3 code, the decimal numbers are incremented by 3 and then written in their bcd format.