Which of these is not likely to result in abnormal chromosome structure?

The answer is D.

There are 4 types of chromosome structural changes.

Deletions, Duplication, Inversion, and Translocation.

the father in the first generation probably had the recessive colorblind trait in his x chromosome. if he and his wife both had the colorblind trait, even if she had 1 recessive and 1 dominant, then that trait would be passed on to their kids.

(since you didn't attach the family tree this is just an assumption)

i believe your answer would be c.. : )