An oxide of iron contains $69.9\%$ iron. Its empirical formula is: (Given: Molar mass of $Fe$ and $O$ are $56$ and $16 \text{ g mol}^{-1}$ respectively.)

In which of the following pairs is the percentage of carbon the same?

Calculate the amount of aluminium present in $Al_2(SO_4)_3$ if the compound contains $4 \text{ g}$ of sulfur. [Molar mass of sulfur = $32 \text{ g/mol}$, Molar mass of $Al = 27 \text{ g/mol}$] (in $\text{ g}$)

In each molecule of carbon tetrachloride,the mass percent of carbon and chlorine respectively are

The percentage of $N_2$ in urea is about

$A$ 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: $Ba = 137 \ amu, Cl = 35.5 \ amu$)