$A$ metal exists as an oxide with formula $M_{0.96} O$. Metal $M$ can exist as $M^{2+}$ and $M^{3+}$ in its oxide $M_{0.96} O$. The percentage of $M^{3+}$ in the oxide is nearly: (in $\%$)

$20 \ g$ of iron pyrite,$FeS_2$,is roasted completely and the $SO_2$ gas produced is absorbed completely in $400 \ mL$ of $NaOH$ solution. If only $50\%$ of the $NaOH$ is used in the reaction,what was the molarity of the $NaOH$ solution?

How many grams of $NaOH$ will be required to prepare $250 \, mL$ of $0.1 \, M$ solution?

What volume (in $mL$) of $0.1 \ M \ KOH$ solution is required for the complete neutralization of $20 \ mL$ of $0.1 \ M$ phosphorous acid $(H_3PO_3)$?

Number of moles of oxygen gas evolved by electrolysis of $180 \ g$ of water?

$1.5 \ mol$ of $O_2$ combine with $Mg$ to form oxide $MgO$. The mass of $Mg$ (atomic mass $24$) that has combined is ............. $g$.