$4 \ g$ of a hydrocarbon on complete combustion gave $12.571 \ g$ of $CO_2$ and $5.143 \ g$ of water. What is the empirical formula of the hydrocarbon?

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

In an organic compound,the weight ratio of $C$,$H$,and $N$ atoms is $9 : 1 : 3.5$. If the molecular weight of the compound is $108$,what is its molecular formula?

Hemoglobin contains $0.34 \%$ of iron by mass. The number of $Fe$ atoms in $3.3 \ g$ of hemoglobin is. (Given : Atomic mass of $Fe$ is $56 \ u, N_A = 6.022 \times 10^{23} \ mol^{-1}$)

$A$ compound contains $2.2 \ g$ of phosphorus and $1.24 \ g$ of sulfur. What is its empirical formula?

$A$ hydrocarbon contains $10.5 \,g$ of carbon and $1 \,g$ of hydrogen. If $2.4 \,g$ of this hydrocarbon occupies a volume of $1 \,L$ at $1 \,atm$ pressure and $127 \,^{\circ}C$ temperature,what is the molecular formula of the hydrocarbon?