An organic compound containing carbon and hydrogen has an empirical formula of $CH_2$. The mass of $1 \ L$ of this organic gas is equal to the mass of $1 \ L$ of $N_2$ gas at the same temperature and pressure. What is the molecular formula of the organic gas?

Complete combustion of $0.858 \ g$ of compound $X$ gives $2.63 \ g$ of $CO_2$ and $1.28 \ g$ of $H_2O$. The lowest molecular mass $X$ can have is ............ $g$.

$A$ 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.

Haemoglobin contains $0.33 \%$ of iron by mass. The molecular mass of haemoglobin is $67200$. The number of iron atoms present in one molecule of haemoglobin is: (Atomic mass of $Fe = 56$)

An organic compound contains $78\%$ (by $wt.$) carbon and the remaining percentage of hydrogen. The correct option for the empirical formula of this compound is: [Atomic $wt.$ of $C$ is $12$,$H$ is $1$]

An organic compound on analysis gives the following data: $C = 57.82 \%$,$H = 3.6 \%$ and the rest is oxygen. Its vapour density is $83$. Calculate its molecular formula.