Which one of the following structures has the IUPAC name $3$-ethynyl-$2$-hydroxy-$4$-methylhex-$3$-en-$5$-ynoic acid?

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.

With respect to the compounds $\mathrm{I}-\mathrm{V}$ choose the correct statement(s).

The correct order of acid strength of the following carboxylic acids is -

The IUPAC name(s) of the following compound is(are)

KI in acetone, undergoes S_N2 reaction with each of P, Q, R and S. The rates of the reaction vary as