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

What does the equation $2Al(s) + \frac{3}{2}O_2(g) \to Al_2O_3(s)$ represent?

Haemoglobin contains $0.33\%$ of iron by weight. The molecular weight of haemoglobin is approximately $67200$. The number of iron atoms (At. wt. of $Fe = 56$) present in one molecule of haemoglobin is

$C_6H_6$ (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 $L$)?

Air contains $23\%$ oxygen and $77\%$ nitrogen by weight. What is the percentage by volume of $O_2$?

One mole of magnesium nitride on the reaction with an excess of water gives