Which one of the following is most reactive towards electrophilic reagent?

Identify $B$ in the following tautomerization reaction:
$4\text{-pyridone} \xrightarrow{KOH} B$

Which of the following optically active compounds has the maximum number of chiral carbons?

Identify the pair of isomers $A$ and $B$ from the given options.

Which of the given statement(s) about $N$, $O$, $P$ and $Q$ with respect to $M$ is (are) correct?
$(A)$ $M$ and $N$ are non-mirror image stereoisomers
$(B)$ $M$ and $O$ are identical
$(C)$ $M$ and $P$ are enantiomers
$(D)$ $M$ and $Q$ are identical

The total number of cyclic structural as well as stereo isomers possible for a compound with the molecular formula $C_5H_{10}$ is