Question

If $N$ is a set of natural numbers, then under binary operation $a ?b =a + b, (N, ?)$ is

• A. quasi-group
• B. semi-group
• C. monoid
• D. group

Answer 1

Answer: (B)

semi-group

Answer 2

The structure (N,) satisfies the closure property, associativity and commutativity but the identity element 0 does not belong to N.
So, N is a semi-group