What type of isomerism is observed between $n$-butyl alcohol and isobutyl alcohol?

Which of the following exhibits metamerism?

What is the minimum number of carbon atoms required to exhibit position isomerism in an organic compound?

Which of the following pairs exhibits the phenomenon of $Metamerism$?

Identify the pairs of compounds which are functional group isomers.
$I$. $CH_3-CH_2-CH_2-CH_2-OH$
$II$. $CH_3-CH_2-CH(OH)-CH_3$
$III$. $(CH_3)_3C-OH$
$IV$. $CH_3-CH(CH_3)-CH_2-OH$
$V$. $CH_3-CH_2-O-CH_2-CH_3$
$VI$. $CH_3-O-CH_2-CH_2-CH_3$
$VII$. $CH_3-O-CH(CH_3)_2$

How many positional isomers are possible for the compound $1,1-dideuterocyclohexane$ shown in the image?