Correct Answer - Option 2 : a + b
Concept
A Prime number is a number divisible by 1 and itself only.
a2 - b2 = (a - b)(a + b)
Calculation
a2 - b2 = (a - b)(a + b) is a prime
So, it is divisible by 1 and itself
So, either (a - b) = 1 or (a + b) = 1
But (a + b) ≠ 1 {a and b are natural numbers}
∴ (a - b) = 1
⇒ a2 - b2 = (1)(a + b) = a + b