The number of isomers of the molecular formula $C_2H_2Br_2$ is:

Which of the following is an isomer of ethanol $(C_2H_5OH)$?

How many structural isomers are possible for $C_3H_6ClBr$ and how many of them are optically active?

What type of isomers are $CH_3-CH_2-O-CH_2-CH_3$ (ethoxy ethane) and $CH_3-O-CH_2-CH_2-CH_3$ (methoxy propane)?

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.

The number of possible structural isomers of $C_3H_4$ is $...$