Functional isomer is not possible for -

Given below are two statements: 

Consider the following four compounds.

(I).
(II).
(III).
(IV).

Which of the following pairs are position isomers?

1. I and II

2. II and III
3. II and IV

4. III and IV

Consider the following four compounds.

I.
II.
III.
IV.

Consider the following pairs of compounds.

(a) II and III

(b) II and IV

(c) I and IV

(d) I and II

Choose the pairs given above that are not functional group isomers:

1. (a, b)

2. (b, c)

3. (c, d)

4. (a, c)