In the binary system, which of the following represents the highest digit?

In the binary system, which is a base-2 numerical system, the only digits used are 0 and 1. Each digit represents a power of two, with 0 indicating the absence of a value and 1 representing the presence of a value.

The concept of "highest digit" in any numbering system refers to the digit that has the greatest value. In binary, since it only employs two digits, 1 is the highest possible digit. A binary number can consist of combinations of these two digits, but the individual digits themselves cannot exceed 1.

On the other hand, the options that include digits such as 2 and 9 do not apply to the binary system, as these are not valid digits in base-2. Therefore, the highest digit in the binary system is definitively 1.