Number of optical isomers possible for $2$-chlorobutane is:

Which one of the following exhibits enantiomerism?

Which one of the following acids does not exhibit optical isomerism?

The optically inactive compound from the following is

An aqueous solution containing compounds $A$ and $B$ shows optical activity. $A$ and $B$ are stereoisomers. Which of the following possibilities cannot be correct?

Which of the following statements is not correct about $(A)$,$(B)$ and $(C)$?