I. `CH_(3) - CH_(2) - CH_(2) - CH_(2) - OH`
II. `CH_(3) - CH_(2) - underset(OH)underset(|)(CH) - CH_(3)`
III. `CH_(3) - underset(OH) underset(|)overset(CH_(3))overset(|)(C) - CH_(3)`
IV. `CH_(3) - underset(CH_(3))underset(|)(CH) - CH_(2) - OH`
V. `CH_(3) - CH_(2) - O - CH_(2) - CH_(3)`
VI. `CH_(3) - O - CH_(2) - CH_(2) - CH_(3)`
VII. `CH_(3) - O - underset(CH_(3))underset(|)(CH) - CH_(3)`
Identify the pairs of compounds which are functional group isomers

Explanation

Two or more compounds having the same molecular formula but different functional groups are called function isomers.
In the given structure, I, II, III, IV represent alcohols as functional group. Whereas V, VI, VII are ethers.
Hence, I and V, I and VI, I and VII, II and VI, II and VI, II adn VII, III and V, III and VI, III and VII, IV and V, IV and VI, IV and VII all are functional group isomers.