Empirical formula of a compound is $CH_2O$ and its vapour density is $30$. The molecular formula of the compound is:

$A$ compound contains $2.34 \ g$ of nitrogen and $5.34 \ g$ of oxygen. What is the empirical formula of the compound?

Arrange the following compounds in the increasing order of percentage of chlorine by weight:
$I.$ $DDT$ $(C_{14}H_9Cl_5)$
$II.$ Gammaxene $(C_6H_6Cl_6)$
$III.$ Carbon tetrachloride $(CCl_4)$
$IV.$ Chlorobenzene $(C_6H_5Cl)$

$A$ carbon compound contains $12.8 \%$ of carbon,$2.1 \%$ of hydrogen and $85.1 \%$ of bromine. The molecular weight of the compound is $187.9$. Calculate the molecular formula of the compound. (Atomic weight: $H=1.008, C=12.0, Br=79.9$)

Among the following,the compound with the highest percentage of chlorine is:

Number of hydrogen atoms per molecule of a hydrocarbon $A$ having $85.8 \%$ carbon is $...............$. (Given : Molar mass of $A = 84 \ g \ mol^{-1}$ )