The percentage composition of carbon by mole in methane is ........... $ \% $

Which of the following has the highest percentage of hydrogen?

In a substance,the number of atoms of $Cr$ and $O$ are $4.8 \times 10^{10}$ and $9.6 \times 10^{10}$ respectively. The empirical formula of the substance is .......

$A$ $64 \, g$ organic compound contains $24 \, g$ of carbon,$8 \, g$ of hydrogen,and the rest is oxygen. The empirical formula of this compound 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: $Ba = 137 \ amu, Cl = 35.5 \ amu$)

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