Total number of isomers of $C_6H_{14}$ are

Tautomerism is exhibited by

Compare the stabilities of the following two compounds :
$A$ : cis-$1$-Ethyl-$3$-methylcyclohexane
$B$ : trans-$1$-Ethyl-$3$-methylcyclohexane

Identify the correct statements from the following. Choose the correct answer from the options given below.
$A$. Pentan$-3-$one and Pentan$-2-$one are metamers.
$B$. Butanenitrile and Butaneisonitrile are functional isomers.
$C$. Butan$-1-$ol and Butan$-2-$ol are position isomers.
$D$. Butan$-1-$amine and $N$-methylpropan$-1-$amine are homologous.

Which of the following is a metamer of the given compound $(X)$?

Which of the following is correctly matched?