$3 \text{ mole}$ of a mixture of $FeSO_4$ and $Fe_2(SO_4)_3$ required $100 \text{ mL}$ of $2 \text{ M}$ $KMnO_4$ solution in acidic medium. Hence,the mole fraction of $FeSO_4$ in the mixture is:

The molarity of pure water is ...... .

For what ratio of volumes should $0.4 \, M \ HCl$ and $0.9 \, M \ HCl$ be mixed to obtain a solution of $0.7 \, M \ HCl$?

$A$ bottle of cold drink contains $200 \ mL$ liquid in which $CO_2$ is $0.1 \ M$. Suppose $CO_2$ behaves like an ideal gas,the volume of the dissolved $CO_2$ at $STP$ is (in $L$)

To neutralize completely $20 \ mL$ of $0.1 \ M$ aqueous solution of phosphorous acid $(H_3PO_3)$,the volume of $0.1 \ M$ aqueous $KOH$ solution required is .......... $mL$.

Sodium oxide reacts with water to produce sodium hydroxide. $20.0 \ g$ of sodium oxide is dissolved in $500 \ mL$ of water. Neglecting the change in volume,the concentration of the resulting $NaOH$ solution is $........ \times 10^{-1} \ M.$ (Nearest integer)
[Atomic mass $: Na=23.0, O=16.0, H=1.0]$