What is the percentage of nitrogen in urea (in $\%$)?

$A$ gaseous hydrocarbon gives upon combustion $0.72 \ g$ of water and $3.08 \ g$ of $CO_{2}$. The empirical formula of the hydrocarbon is:

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

$A$ gas is found to contain $2.8 \ g$ of nitrogen and $3.2 \ g$ of oxygen. The simplest formula of the compound is:

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

$A$ sample of a hydrate of barium chloride weighing $61 \ g$ was heated until all the water of hydration was removed. The dried sample weight is $52 \ g$. The formula of the hydrated salt is: (atomic mass: $Ba = 137 \ amu, Cl = 35.5 \ amu$)