The children of a colour-blind mother and a normal father will be
[a] normal daughters and sons[b] normal sons and carrier daughters[c] colour blind sons and carrier daughters[d] colour blind sons and daughters

Choice C. Color blindness affects the X chromosome. The children will get one X color blind chromosome from the mother (who has two color blind X chromosomes). For a boy, he will get a Y from the father and be color blind. A girl will get a healthy X chromosome from the father and be a carrier.