$20.0 \ g$ of a magnesium carbonate sample decomposes on heating to give carbon dioxide and $8.0 \ g$ magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? $(At. \ wt. \ of \ Mg = 24)$

$23 \ g$ of sodium will react with methyl alcohol to give

$C_6H_6$ (liq) + $\frac{15}{2}O_2$ $(g)$ $\rightarrow$ $6CO_2$ $(g)$ + $3H_2O$ (liq). Benzene burns in oxygen according to the above equation. What is the volume of oxygen (at $STP$) needed for complete combustion of $39 \ g$ of liquid benzene (in $L$)?

The volume in $mL$ of $0.1 \ M$ solution of $NaOH$ required to completely neutralize $100 \ mL$ of $0.3 \ M$ solution of $H_3PO_3$ is

Given that $N_{2(g)} + 3 H_{2(g)} \longrightarrow 2 NH_{3(g)}$; $\Delta_r H^{\circ} = -92 \ kJ$, the standard molar enthalpy of formation in $kJ \ mol^{-1}$ of $NH_{3(g)}$ is

$A$ gas mixture contains $25 \%$ He and $75 \% CH_4$ by volume at a given temperature and pressure. The percentage by mass of methane in the mixture is approximately . . . . . . (in $\%$)