The density of a gas at $STP$ is $2.86 \, g \, L^{-1}$. Which of the following is the gas?

$250 \ mL$ of a sodium carbonate solution contains $2.65 \ g$ of $Na_2CO_3$. If $10 \ mL$ of this solution is diluted to $1 \ L$,what is the concentration of the resultant solution (in $M$)?

$A$ $250 \, mL$ solution of sodium carbonate contains $5.3 \, g$ of $Na_2CO_3$. If $10 \, mL$ of this solution is taken and diluted with distilled water to $0.1 \, L$,what will be the concentration of the resulting solution?

For a reaction,$N_2O_{5(g)} \rightarrow 2NO_{2(g)} + \frac{1}{2}O_{2(g)}$ in a constant volume container,no products were present initially. The final pressure of the system when $50\%$ of the reaction is completed is:

$20 \, mL$ of a $1 \, N$ solution of $KMnO_4$ just reacts with $20 \, mL$ of a solution of oxalic acid. The weight of oxalic acid crystals in $1 \, L$ of the solution is $... \, g$

The molecular formula of a commercial resin used for exchanging ions in water softening is $C_8H_7SO_3^- Na^+$ $(Mol. \ wt. 206)$. What would be the maximum uptake of $Ca^{2+}$ ions by the resin when expressed in mole per gram resin?