x is a positive integer.
I. Given : x is a prime number.
GCD (2, 300) = 2 (prime)
GCD (Any prime no. other than 2, 300) = 1 (Non - Prime)
⇒ GCD may or may not be prime.
∴ I alone is not sufficient.
II. Given x > 5
GCD (6, 300) = 6 (Non - prime)
GCD (22,300) = 2 (Prime).
∴ II alone not sufficient.
I & II.
x is a prime number greater than 5.
GCD (A prime no. greater than 5,300) = 1 (Non-prime)
∴ I & II together are sufficient.