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:

40 mL of a mixture of $\mathrm{CH}_3 \mathrm{COOH}$ and HCl (aqueous solution) is titrated against 0.1 M NaOH solution conductometrically. Which of the following statement is correct?

X g of nitrobenzene on nitration gave 4.2 g of m -dinitrobenzene. X = __________g. (nearest integer)

[Given : molar mass (in $\left.\left.\mathrm{g} \mathrm{mol}^{-1}\right) \mathrm{C}: 12, \mathrm{H}: 1, \mathrm{O}: 16, \mathrm{~N}: 14\right]$