Why these answers are so?

Question

1- For this reaction 2H2 + O2 = 2H2O
a- dela H=delta Hf
b-delta Hc= delta Hf
c- delta H= delta Hc
d- delta S= delta H
and the answer is b , but how and why?

2- For this reaction 2S + 3O2 = 2SO3 + 792 kJ
which of the following isn't correct
a- delta Hc of S = delta Hf of SO3
b- delta H # delta Hf of SO3
c- The reaction is exothermic
d- delta H = delta Hc of S
and the answer is d , how?

3- Whic of the following about this reaction is correct
CO + 1/2 O2 = CO2
a- delta Hf of CO2 = delta H
b- delta H = delta Hc of CO
c- delta Hf of CO2 = delta Hc of CO
d- the heat of reaction and the entropy is equal
and the answer is b , how and why?

Please help me, thank you a lot