Catalytic hydrogenation of phenyl diazonium bromide produces

Catalytic hydrogenation of the following compound produces saturated hydrocarbon(s). The number of stereoisomer(s) formed is :

Catalytic hydrogenation of the following compound produces saturated hydrocarbon(s). The number of stereoisomer(s) formed is :

Explain catalytic hydrogenation.

The relative rate of catalytic hydrogenation of the following alkenes is :