Question

which set of numbers does -7 belong

Answer 1

Natural numbers.

Answer 2

No. Not natural numbers.

Natural numbers (same as counting numbers): {1, 2, 3, 4, 5, 6, ...}
Whole numbers: {0, 1, 2, 3, 4, 5, 6, ...}
Integers: {..., -3, -2, -1, 0, 1, 2, 3, ...}