01. WHOLE NUMBERS
Explanation:
0
Solution:
An additive identity is a number which when added to any number, the number is unchanged.
For example: 0 + 7 = 7, 0 + 9 = 9, 0 + (- 11) = -11 etc.
Thus, 0 is the additive identity in the set of whole numbers.
Hence, the correct option is (a).