Given below are two statements :

Statement I : Mohr's salt is composed of only three types of ions-ferrous, ammonium and sulfate.

Statement II : If the molar conductance at infinite dilution for ferrous, ammonium and sulfate ions are $x_1, x_2$ and $x_3 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$, respectively then the molar conductance for Mohr's salt solution at infinite dilution would be given by $x_1+x_2+2 x_3$

In the light of the given statements, choose the correct answer from the options given below :

When a salt is treated with sodium hydroxide solution it gives gas X . On passing gas X through reagent Y a brown coloured precipitate is formed. X and Y respectively, are

Compounds that should not be used as primary standards in titrimetric analysis are :

A. $\mathrm{Na}_2 \mathrm{Cr}_2 \mathrm{O}_7$

B. Oxalic acid

C. NaOH

D. $\mathrm{FeSO}_4 \cdot 6 \mathrm{H}_2 \mathrm{O}$

E. Sodium tetraborate

Choose the most appropriate answer from the options given below: