ElGamal Generator g problem Having an ElGamal encryption scheme with p=19 which value can not be assigned to
g?

The answers were :  1,7,11,2

I think you can't assign value 1 to g.
We can choose a generator which is a primitive root. We can check that 1,7,11,12 are not primitive roots for p=19. So they cannot be chosen as a generator.Given any number we can check if it is a primitive root or not.
(https://math.stackexchange.com/questions/124408/finding-a-primitive-root-of-a-prime-number).