Which of the following statements is not true about Mohr's salt?

$10 \, mL$ of concentrated $HCl$ were diluted to $1 \, L$. $20 \, mL$ of this diluted solution required $25 \, mL$ of $0.1 \, N$ sodium hydroxide solution for complete neutralization. The normality of the concentrated hydrochloric acid will be:

The reagent commonly used to determine the hardness of water titrimetrically is

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:

$K_2Cr_2O_7$ is preferred over $Na_2Cr_2O_7$ for use in volumetric analysis as a primary standard because

$KMnO_4$ is titrated with ferrous ammonium sulphate hexahydrate in the presence of dilute $H_2SO_4$. The number of water molecules produced for $2$ molecules of $KMnO_4$ is $..........$.