The most stable conformer of n-butane is anti butane.

For the given compound X, the total number of optically active stereoisomers is ____.

Identify $A$ in the given chemical reaction.

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$