Propyne and propene can be distinguished by

A compound $\mathrm{X}\hspace{0.17em}\left({\mathrm{C}}_5{\mathrm{H}}_8\right)$ reacts with ammoniacal ${\mathrm{AgNO}}_3$ to give a white precipitate, and on oxidation with hot alkaline ${\mathrm{KMnO}}_4$ gives the acid, $({\mathrm{CH}}_3{)}_2\mathrm{CHCOOH}$. Therefore, $\mathrm{X}$ is 

X is?

$\mathrm{CH} \equiv \mathrm{CH} \stackrel{{\mathrm{O}}_3}{\to } \mathrm{X} \stackrel{\mathrm{Zn}/{\mathrm{CH}}_3\mathrm{OH}}{\to } \mathrm{Y}, \mathrm{Y}$ is

The molecular formula of diphenylmethane, ${\mathrm{C}}_{13}{\mathrm{H}}_{12}$ is  

How many structural isomers are possible when one of the hydrogens is replaced by a chlorine atom?