How many moles of ethene are required to prepare $6.0 \ g$ of ethane by the hydrogenation process (in $mole$)?

What is $\Delta n$ for the combustion of $1 \ mole$ of benzene,when both the reactants and the products are in the gaseous state at $298 \ K$?

In a chemical reaction, the sum of the formula weights of all reactants is $274 \text{ u}$ and the atom economy is $50\%$. Calculate the formula weight of the desired product. (in $\text{ u}$)

What volume of $O_{2(g)}$ measured at standard condition will be formed by the action of $100 \ mL$ of $0.5 \ N \ KMnO_4$ on hydrogen peroxide in an acidic solution? The skeleton equation for the reaction is:
$KMnO_4 + H_2SO_4 + H_2O_2 \to KHSO_4 + MnSO_4 + O_2 + H_2O$
(Answer in $L$)

$20.0 \ g$ of a magnesium carbonate sample decomposes on heating to give carbon dioxide and $6.0 \ g$ magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? (Atomic weight of $Mg = 24$)

The number of chlorine atoms in $20 \, mL$ of chlorine gas at $STP$ is ..... $\times 10^{21}$. (Round off to the Nearest Integer).
[Assume chlorine is an ideal gas at $STP$,$R = 0.083 \, L \, bar \, mol^{-1} \, K^{-1}$,$N_{A} = 6.023 \times 10^{23}$]