why cant 7 be the difference of any prime number?

Question

 i have to prove why 7 cant be the difference of any prime number

Answer 1

All primes other than 2 are odd numbers. If two primes are odd, the difference should be even, so not 7. If one of the prime is 2, the other prime has to be 9 which is not a prime. So 7 can't be the difference of any prime numbers.