If two compounds have the same empirical formula but different molecular formulae,they must have:

In the crystalline solid $MSO_{4} \cdot nH_{2}O$ of molar mass $250 \ g \ mol^{-1}$, the percentage of anhydrous salt is $64$ by weight. The value of $n$ is

In a compound made of $X$ and $Y$,their masses are equal. If the atomic masses of $X$ and $Y$ are $30$ and $20$ respectively,then the molecular formula of the compound will be ......... (Its molecular mass $= 120$).

The percentage of $Se$ in peroxidase enzyme is $0.5\%$ by mass (atomic mass of $Se = 78.4 \ amu$). Then,the minimum molecular mass of enzyme which contains not more than one $Se$ atom is

The molecular mass of caffeine is $194 \, a.m.u.$. It contains $28.9 \%$ of nitrogen by mass. The number of nitrogen atoms in one molecule of caffeine is ...............

Urea is a better fertilizer than ammonium sulphate because