The molarity of $1 \ L$ orthophosphoric acid $(H_3PO_4)$ having $70 \%$ purity by weight (specific gravity $1.54 \ g \ cm^{-3}$) is $ . . . . . . $ $M$.
(Molar mass of $H_3PO_4 = 98 \ g \ mol^{-1}$)

The vapour density of a certain gas is $16$. What is the volume occupied by $8 \ g$ of gas at $STP$ assuming ideal behaviour (in $dm^3$)?

What is the stoichiometric ratio of the products in the reaction: $3K_2MnO_4 + 2H_2SO_4 \rightarrow 2KMnO_4 + 2K_2SO_4 + MnO_2 + 2H_2O$?

The normality of a $1 \ M$ $H_3PO_4$ solution is ........ $N$.

Dissolving $1.24 \ g$ of white phosphorus in boiling $NaOH$ solution in an inert atmosphere gives a gas $Q$. The amount of $CuSO_4$ (in $g$) required to completely consume the gas $Q$ is. . . . [Given: Atomic mass of $H = 1, O = 16, Na = 23, P = 31, S = 32, Cu = 63$]

Given the ratio of masses of nitrogen and oxygen in a particular gaseous mixture is $4: 1$. Calculate the ratio of the number of their molecules.