Zero (0) is

Whenever a number is added to Zero (0) the number obtained is a the same rational number to which it is added.

(b) Incorrect because if we subtract a rational number from 0 the number obtained will not be the same number.

(c) Incorrect because if we multiply 0 with a rational number the number obtained will be 0 and not the number to which 0 was multiplied.

(d) Incorrect because when a number is divided by 0 the result will be undefined.