Which one of the following pairs of compounds are functional isomers?

Which of the following pairs of compounds are positional isomers?

$o-$Cresol and benzyl alcohol are .... of each other.

Given below are two statements :
Statement $(I) :$ $CH_3CH=CHCH_3$ and $cyclobutane$ are isomeric compounds.
Statement $(II) :$ $CH_3CH_2CH_2CH_2NH_2$ and $(CH_3CH_2)_2NH$ are functional group isomers.
In the light of the above statements,choose the correct answer from the options given below :

What is the relationship between the following two structures?
$1. CH_3-CH_2-CO-CH_2-CH_3$
$2. CH_3-CH_2-CH_2-CH_2-CHO$

Number of metamers represented by molecular formula $C_4H_{10}O$ is