$A$ $0.166 \ g$ sample of an organic compound was digested with conc. $H_2SO_4$ and then distilled with $NaOH$. The ammonia gas evolved was passed through $50.0 \ mL$ of $0.5 \ N \ H_2SO_4$. The excess acid required $30.0 \ mL$ of $0.25 \ N \ NaOH$ for complete neutralization. The mass percentage of nitrogen in the organic compound is $..... \ \%$.

The primary standard solution for the estimation of $Na_2S_2O_3$ is:

What weight of ferrous ammonium sulphate is needed to prepare $100 \, mL$ of $0.1 \, N$ solution? (mol. wt. $392$)

$30 \ mL$ of acid solution is neutralized by $15 \ mL$ of a $0.2 \ N$ base. The strength of acid solution is $.............. \ N$.

Below are two statements. One is labeled as Assertion $(A)$ and the other as Reason $(R).$
Assertion $(A):$ When using an aqueous solution of $KOH$ in a volumetric analysis,its concentration should be checked before use.
Reason $(R):$ $KOH$ solution absorbs atmospheric $CO_2$ when it gets old.
In the context of the above statements,choose the correct answer from the options given below:

$FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O$ is called: