Two compounds $\mathrm{X} \mathrm{and} \mathrm{Y}$ are enantiomers of each other.

Name one physical property that:

(i) is the same for $\mathrm{X} \mathrm{and} \mathrm{Y}$.

(ii) is different for $\mathrm{X} \mathrm{and} \mathrm{Y}$.

Which of the following alkenes can generate optically active compounds upon hydrogenation?

The Fischer projection of $\mathrm{D}$-erythrose is shown below.

$\mathrm{D}$-Erythrose and its isomers are listed as $\mathrm{P},\mathrm{Q},\mathrm{R},$ and $\mathrm{S}$ in Column I. Choose the correct relationship of $\mathrm{P},\mathrm{Q},\mathrm{R},$ and $\mathrm{S}$ with $\mathrm{D}$-erythrose from Column II.

	Column - I		Column -II
P.		1.	Diastereomer
Q.		2.	Identical
R.		3.	Enantiomer
S.