$A$ $400 \ mg$ iron capsule contains $100 \ mg$ of ferrous fumarate,$(C_2H_2O_4)Fe$. The percentage of iron present in it is approximately $.......... \%$.

$20$ carat gold contains ...... $(\%)$ percent gold.

An organic compound contains $78\%$ (by $wt.$) carbon and the remaining percentage of hydrogen. The correct option for the empirical formula of this compound is: [Atomic $wt.$ of $C$ is $12$,$H$ is $1$]

$4 \ g$ 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?

$A$ certain compound has the molecular formula $X_4O_6$. If $10 \ g$ of $X_4O_6$ has $5.72 \ g$ of $X$,the atomic mass of $X$ is ............ $amu$.

An organic compound containing carbon,hydrogen,and oxygen contains $52.20\%$ carbon and $13.04\%$ hydrogen. The vapour density of the compound is $23$. Its molecular formula will be: