$10 \ cm^{3}$ of $0.1 \ N$ monobasic acid requires $15 \ cm^{3}$ of sodium hydroxide solution whose normality is: (in $N$)

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

Identify the correct statements:
$A$. Hydrated salts can be used as primary standard.
$B$. Primary standard should not undergo any reaction with air.
$C$. Reactions of primary standard with another substance should be instantaneous and stoichiometric.
$D$. Primary standard should not be soluble in water.
$E$. Primary standard should have low relative molar mass.
Choose the correct answer from the options given below :

The volume of $\frac{N}{10}$ $NaOH$ required to neutralize $100 \ mL$ of $\frac{N}{25}$ $HCl$ is......$mL$

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

In the standardization of $Na_2S_2O_3$ using $K_2Cr_2O_7$ by iodometry,the equivalent weight of $K_2Cr_2O_7$ is