(a) a prime number
2 is a prime number because it has exactly two distinct factors: 1 and itself, and it is listed among the collection of prime numbers in the Fundamental Theorem of Arithmetic.
Source: Chapter 1, Section 1.2
2 is the smallest and the only even prime number. A prime number has exactly two factors — 1 and itself. 2 satisfies this condition. It is neither composite (which requires more than two factors) nor both. Examiners expect the correct option with a brief justification for MCQs.