In the catalytic reduction of hydrocarbons,which catalyst is mostly used?

An alkene $A$ on reaction with $O_{3}$ and $Zn-H_{2}O$ gives propanone and ethanal in equimolar ratio. Addition of $HCl$ to alkene $A$ gives $B$ as the major product. The structure of product $B$ is:

Which one is an unsaturated compound?

Addition of $Br_2$ to $cis$-$2$-butene would give a product which is

Which $\pi$-bond will be reduced first when the compound shown below undergoes catalytic hydrogenation?

Choose the correct option for the following reactions.