I have been doing practice problems in General Organic Chemistry. I got some questions that asked me to compare the Heat of Combustion of some molecules. I couldn't get any of those questions and the logic behind their answers. I tried googling but it didn't help. The search results were not direct. So, I'd like to know the factors on which the heat of hydrogenation depends. I am not looking for an answer that describes it quantitatively but rather qualitatively.
Here are some example questions:
The answer is (c). But why is that?
The answer is 2>4>1>3. But again, why is that?
I knew that the heat of combustion depends on the number of carbon atom. But in these two examples the number of carbon atoms are same. Is there anything I need to watch out for?