Dear student
This is a little tricky; you can't get 1-butanol by using ethyl magnesium bromide to attack a carbonyl, because the -OH group ends up in the wrong place. You need to attack something else: an epoxide.
A Grignard will open an epoxide ring, giving an anionic oxygen that can be protonated. If you attack ethylene oxide, also called oxirane, with ethyl magnesium bromide, you'll get 1-butanol.
Regards
Arun (askIITians forum expert)