Sir Why natural nos can be called as whole nos but whole no's cannot be called as natural no's.
My second question--> Why can't odd even composite and prime nos are the part of no. system because in no system there are only natural, whole, integers, rational, irrational, real no's.
I assume by "whole number" you mean "integer". If this is not the case, ask a follow-up and define "whole number."
Natural numbers are the numbers we use for counting: 1, 2, 3, ... (0 may or may not be included depending on the school of thought).
Integers include 0 and negative numbers: ..., -2, -1, 0, 1, 2, ...
Odds, evens, composites, and primes are part of the number system, but we don't usually call them out the way we do for natural, integers, or reals. The circumstances where we need to collectively refer to the naturals, integers, and reals are much more common than having to refer to the others.
That said, if you take some higher mathematics courses such as abstract algebra or number theory, you may see the sets of odds, evens, composites, and primes explicitly referred to.
Thanks for asking,