Which of these square numbers cannot be expressed as the sum of two prime numbers?

Correct option is C

Solution:

Consider 49: It can be written as 2 + 47, both of which are prime numbers.
For 81: It equals 2 + 79, both of which are also primes.
Now, take 121: It can be expressed as 2 + 119, but 119 is not a prime number since it is the product of 7 and 17. Additionally, no other pair of primes adds up to 121 because the sum of two odd primes would be even, while 121 is odd.
Finally, for 144: It can be expressed as 3 + 141, or as 5 + 139, 7 + 137, and 13 + 131—all of which include prime numbers.
Therefore, out of the given square numbers, 121 is the only one that cannot be expressed as the sum of two prime numbers.