$A$ pure compound contains $2.4 \ g$ of $C$,$1.2 \times 10^{23}$ atoms of $H$,and $0.2 \ mol$ of oxygen atoms. Its empirical formula is

$A$ sample of a pure compound contains $1.15 \ g$ of sodium,$3.01 \times 10^{22}$ atoms of carbon,and $0.1 \ mol$ of oxygen atoms. Its empirical formula is:

$A$ hydrocarbon contains $80\% \ C$. The vapour density of the compound is $30$. The molecular formula of the compound is :-

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 $Fe = 56 \ g/mol$)

The molecular formula of potash alum is

The correct sequence in decreasing order of the percentage of nitrogen in the given compounds is