Question

All isomers of butanone

Answer 1

There are the 2 ketones you mention - butan-1-one and butan-2-one but there are more 

eg unsaturated alcohols 

C=C-C-C-OH - 3-butene-1-ol 

C-C=C-C-OH - 2-butene-1-ol 

C=C-C(OH)-C - 1-butene -3-ol 

unsaturated esters 

C=C-C-O-C 

C-C(=C)-O-C 

C=C-O-C-C 

Answer 2

Answer:

There are only two isomers, and they are 1-butanal and 2-methylpropanal. "3-methylpropanal" is identical to 1-butanal. "2-butanone" is not an aldehyde anymore, but a ketone.