An organic compound has an empirical formula $CH_2O$,its vapour density is $45$. The molecular formula of the compound is

$4 \ g$ of a hydrocarbon on complete combustion gave $12.571 \ g$ of $CO_2$ and $5.143 \ g$ of water. What is the empirical formula of the hydrocarbon?

Two oxides of a metal $X$ contain $50 \%$ and $40 \%$ of oxygen respectively. If the formula of the first oxide is $XO_2$,then the formula of the second oxide is:

Calculate the percentage composition of element $P$ in ${H_3PO_4}$. (in $\%$)

Hemoglobin in red blood cells contains $0.33\%$ iron by mass. The molecular weight of hemoglobin is $67000$. What is the number of iron atoms present in each molecule of hemoglobin? (Atomic mass of $Fe = 56 \ g/mol$)

An organic compound contains $C = 38.8\%$,$H = 16\%$ and $N = 45.2\%$. The empirical formula of the compound is: