Bunuel wrote:

If a and b are prime numbers, is ab even?

(1) The sum of a and b is prime

(2) The difference of a and b is prime

Points to keep in mind are:-

a) only even prime is 2

b)all primes are odd except 2

c) 0 & 1 is not a prime number.

d) -ve numbers are not primes

Statement (1)

The sum of a and b is prime

it means sum of 2 numbers is odd since a & b are both primes.

Now as even +odd=odd so for prime numbers family we have only one even number is 2 thus ab is even

But for any other primes than 2 obviously which are ODD we get odd+odd=even (not a prime).....suff.

Statement (2)

let a=5 and b=2 than difference is 3 (prime).......YES

let a=13 and b=11 than difference is 2 (prime).......NO............insuff

Ans A