A number a satisfies HCF(a, 240) = 16.
Which of these can NOT be the value of a?

The HCF divides BOTH numbers, so 16 must divide a. Now $112=16\times 7,176=16\times 11$ and $208=16\times 13$ each give HCF exactly 16 with $240=16\times 15$. But $200=2^3\times 5^2$ is not a multiple of 16 - in fact HCF(200, 240) = 40 - so 200 is impossible.