Correct Answer - Option 4 : 16

For any number system with the radix (base) r, the allowed numbers are from 0 to (r – 1).

- For the binary system, the radix is 2 and the numbers used in this system are 0 and 1
- For the octal system, the radix is 8 and the numbers used in this system are 0 to 7
- For the decimal system, radix is 10 and the numbers used in this system are 0 to 9
- For the Hexadecimal system, radix is 16 and the numbers used in this system are 0 to F