Which of the following alkenes is the most stable?

Identify $A$ in the reaction:

What is the major product of the following reaction?
Cyclopentene + $D_2$ $\xrightarrow{Pd}$ ?

The compounds that will give an isomer of $2,2$-dimethylpropane on catalytic hydrogenation are:
$(1)$ $CH_3-CH=C(CH_3)_2$
$(2)$ $CH_3-CH=CH-CH_3$
$(3)$ $CH_3-CH=CH-CH_2-CH_3$
$(4)$ $CH_3-C(CH_3)=C(CH_3)-CH_3$

Find the major product for the reaction shown below.

Which one of the following alkenes when treated with $HCl$ yields majorly an anti-Markovnikov product?