Which of the following may exist in enantiomorphs?

Which of the following compounds is an optically active substance with a low molecular weight?

The correct statement$(s)$ about compounds $A$,$B$,and $C$ is/are:

The Fischer projection of $D$-erythrose is defined by the structure $CHO-C(OH)(H)-C(OH)(H)-CH_2OH$ with both hydroxyl groups on the right. $D$-Erythrose and its isomers are listed as $P, Q, R,$ and $S$ in Column-$I$. Choose the correct relationship of $P, Q, R,$ and $S$ with $D$-erythrose from Column-$II$.
Column-$I$:
$P$: $CHO-C(OH)(H)-C(OH)(H)-CH_2OH$ (rotated)
$Q$: $CHO-C(H)(OH)-C(OH)(H)-CH_2OH$
$R$: $CHO-C(OH)(H)-C(H)(OH)-CH_2OH$
$S$: $CHO-C(H)(OH)-C(H)(OH)-CH_2OH$ (enantiomer)
Column-$II$:
$1$. Diastereomer
$2$. Identical
$3$. Enantiomer

Which of the following acids does not exhibit optical isomerism?

Pure $(S)-2-$butanol has a specific rotation of $+13.52^{\circ}$. $A$ sample of $2-$butanol prepared in the lab and purified by distillation has a calculated specific rotation of $+6.76^{\circ}$. What can you conclude about the composition?