The empirical formula of a compound is $CH_2O$ and its molecular weight is $120$. The molecular formula of the compound is:

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

Calculate the mass of $Ca$ in $g$ present in $Ca(NO_3)_2$ that contains $20 \ g$ of nitrogen.

$A$ welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives $3.38 \, g$ of carbon dioxide,$0.690 \, g$ of water,and no other products. $A$ volume of $10.0 \, L$ (measured at $STP$) of this welding gas is found to weigh $11.6 \, g$. Calculate:
$(i)$ empirical formula,
$(ii)$ molar mass of the gas,and
$(iii)$ molecular formula.

If we want to study the relative arrangement of atoms in a molecule,we study:

An organic compound contains $C = 36\%$,$H = 6\%$ and the rest is oxygen. Its empirical formula is: