just answer some basics

C is most stable of the four alkenes...

Q2. Last one

for Q1: lower the enthalpy of hydrogenation, stabler the alkene.
Moreover, 'An alkene is stabilised by alkyl substituents on the double bond". This means C is the stablest among'em all. That's why consequently highest heat of hydrogenation.

ur answers r correct asish
my doubt z due to which effect C z more stable thn D

2......D>B>C>A