If a boy's father has haemophilia and his mother has one gene for haemophilia; what is the chance that the boy will inherit the disease

Haemophillic man marries a normal woman. Their offsprings will be

Given below is a highly simplified representation of the human sex chromosomes from a karyotype.

The genes $a$ and $b$ could be of

Which one is the incorrect statement with regard to the importance of pedigree analysis?

A woman with normal vision, but whose father was colour blind, marries a colour blind man. Suppose that the fourth child of this couple was a boy. Thus boy