Under closure property, adding some whole numbers –
2 + 9 = 11, Whole number
8 + 15 = 23, Whole number
14 + 3 = 17, Whole number
16 + 4 = 20, Whole number
11 + 7 = 18, Whole number
Yes, on adding whole numbers, result is always whole number.
No, there is no pair whose sum is not a whole number.