Question

What would stars be like if carbon had the smallest mass per nuclear particle?

Answer 1

If carbon had the smallest mass per nucleon many common fusion reactions couldn't exist.

Explanation:

Nuclear fusion only produces energy if the binding energy per nucleon is reduced as a result of the reaction. In our universe, `"iron"` is the element which is at the limit.

If carbon had the lowest binding energy per nucleon, all elements heavier than carbon could only be produced as a result of a `"supernova explosion."`

The main effect on stars would be that they would have much shorter lifetimes as once fusion created carbon any further fusion reactions would not be possible.