$A$ metal oxide contains $75 \%$ metal by mass. If the vapour density of the metal chloride is $89$,what is the atomic weight of the metal?

What quantity (in $mL$) of a $45\%$ acid solution of a mono-protic strong acid must be mixed with a $20\%$ solution of the same acid to produce $800 \ mL$ of a $29.875\%$ acid solution?

Natural gas is a mixture of methane and ethane. The heat produced by the complete combustion of $10 \, L$ of this mixture at $S.T.P.$ is $476.6 \, kJ$. Given $\Delta H_{comb} (CH_4) = -894 \, kJ \, mol^{-1}$ and $\Delta H_{comb} (C_2H_6) = -1500 \, kJ \, mol^{-1}$,calculate the percentage of methane and ethane in the mixture by volume.

The density of a liquid is $1.5 \, g/mL$. There are $50 \, drops$ in $5 \, mL$. The number of molecules in $1 \, drop$ is (molecular weight of liquid is $100$).

$1 \, L$ aqueous solution of $H_{2}SO_{4}$ contains $0.02 \, mmol$ $H_{2}SO_{4}$. $50 \%$ of this solution is diluted with deionized water to give $1 \, L$ solution $(A)$. In solution $(A)$,$0.01 \, mmol$ of $H_{2}SO_{4}$ are added. Total $mmol$ of $H_{2}SO_{4}$ in the final solution is $...... \times 10^{-3} \, mmol$.

If $2.4088 \times 10^{21}$ molecules are removed from $392 \, mg$ of $H_2SO_4$ in a container,the number of $H_2SO_4$ molecules remaining in the container will be ........