The total number of structural isomers possible for the substituted benzene derivatives with the molecular formula $\mathrm{C}_9 \mathrm{H}_{12}$ is________.

The hydrocarbon $(\mathrm{X})$ with molar mass $80 \mathrm{~g} \mathrm{~mol}^{-1}$ and $90 \%$ carbon has _______ degree of unsaturation.

The possible number of stereoisomers for 5-phenylpent-4-en-2-ol is ________.

In Carius method for estimation of halogens, 180 mg of an organic compound produced 143.5 mg of AgCl . The percentage composition of chlorine in the compound is _________ %. (Given : molar mass in $\mathrm{g} \mathrm{~mol}^{-1}$ of $\mathrm{Ag}: 108, \mathrm{Cl}: 35.5$ )