(A) Natural numbers:
A set of counting numbers is called natural numbers.
N = {1,2,3,4,5,...}
Whole number :
A set of natural numbers along with zero is called whole numbers.
W= {0,1,2,3,4,5,....}
So, All natural numbers are whole numbers but all whole numbers are not natural numbers.
So, (A) is correct.
(B) Every integer, natural and whole number is a rational number (not irrational numbers) as they can be expressed in terms of

.
So, (B) is incorrect
(C) All rational and all irrational numbers make a collection of real numbers. It is denoted by the letter R .
So, (C) is correct.
(D) Let n – 1 and n be two consecutive positive integers.
Then their product is n (n – 1) = n
2 – n.
We know that every positive integer is of the form 2q or 2q + 1 for some integer q.
So, let n = 2q
So,
n
2 – n
= (2q)
2– (2q)
= 4q
2 – 2q
= 2q (2q – 1)
= 2r [where r = q(2q – 1)]
n
2 - n is even and divisible by 2.
Let n = 2q + 1
So,
n
2 – n = (2q + 1)
2– (2q + 1)
= (2q + 1) ((2q + 1) – 1)
= (2q + 1) (2q)
= 2r[r = q (2q + 1)]
n
2 – n is even and divisible by 2 and not by 3.
So, (D) is incorrect.