Which of the following pairs are not funtional group isomers?

(I) 

(II) 

(III) 

(IV) 

1.  II and IV

2.  II and IV

3.  I and IV

4.  I and II


(a, c)
Two or more compounds having the same molecular forumla but different functional groups are called functional isomers.
I. Aldehyde
II. Ketone
III. Ketone
IV. Aldehyde
Here, II and II; I and IV are not functional group isomers. Thus, option (a) and (c) are correct.