Which one of the following statements is not true?

(A) 25 is a perfect square.

(B) 31 is a prime number.

(C) 3 is the smallest prime number.

(D) 8 is a perfect cube.

(E) 15 is the product of two prime numbers.
We look at each of the five statements.

25 is a perfect square, since $25=5^{2}$.

31 is a prime number, since it has no positive factors other than 1 and 31.

3 is not the smallest prime number, since 2 is a prime number.

8 is a perfect cube, since $8=2^{3}$.

15 is the product of two prime numbers, since $15=3 \times 5$.

ANSWER: (C)