The function f:N→N  given by f(x) = x² is-

injective but not surjective

f:N→N   is given by f(x) = x²

It is seen that for x, y ∈ N , f(x) = f(y)  ⇒ x² = y² ⇒ x =y

So f is injective.

Now, 2 ∈ N, But there does not exist any element x in N such that f(x) = x² = 2

so f is not surjective.

Hence, function f is injective but not surjective.