Which equilibrium is not rapid at room temperature?

Match List-$I$ with List-$II$.

List-$I$ (Pair of Compounds)	List-$II$ (Type of Isomers)
$A$. $2-$Methylpropene and but$-1-$ene	$I$. Stereoisomers
$B$. $Cis-$but$-2-$ene and $trans-$but$-2-$ene	$II$. Position isomers
$C$. $2-$Butanol and diethyl ether	$III$. Chain isomers
$D$. But$-1-$ene and but$-2-$ene	$IV$. Functional group isomers

Choose the correct answer from the options given below:

$P$ and $Q$ are isomers of dicarboxylic acid $C_4H_4O_4$. Both decolorize $Br_2/H_2O$. On heating,$P$ forms a cyclic anhydride.
Upon treatment with dilute alkaline $KMnO_4$,$P$ as well as $Q$ could produce one or more than one from $S$,$T$,and $U$.
$1.$ Compounds formed from $P$ and $Q$ are,respectively:
$(A)$ Optically active $S$ and optically active pair $(T, U)$
$(B)$ Optically inactive $S$ and optically inactive pair $(T, U)$
$(C)$ Optically active pair $(T, U)$ and optically active $S$
$(D)$ Optically inactive pair $(T, U)$ and optically inactive $S$
$2.$ In the following reaction sequences,$V$ and $W$ are respectively:
Give the answer for question $1$ and $2$.

Which of the following is a meso compound?

Which energy diagram best represents the given reaction?

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