Compounds having same molecular formula but different connectivity of atoms or groups are called structure isomers. Structrue isomers are futher classify according to their dissimilarities.
Which is not the isomer of butanoic acid?
A. `3`-Hydroxybutanal
B. Ethyl ethanoate
C. `2`-Methylpropanoic acid
D. Butane-`2,3`-diol