Lactic acid,in which a methyl group,a hydroxyl group,a carboxylic acid group,and a hydrogen atom are attached to a central carbon atom,shows optical isomerism due to the molecular geometry at the:

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

Which type of isomerism is exhibited by the given compound?
$(CH_3)_2C=CH-CH(CH_3)COOH$

Non-superimposable mirror images are called.........

The Fischer projection of $D$-erythrose is shown below.
$D$-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 pairs of $2,3-$butanediol are enantiomers?