Which of the following is true about nuclear fusion in stars?

a
When hydrogen atoms merge to form helium atoms, the helium atoms have slightly less mass than the hydrogen atoms that combined to make them
b
When helium atoms split apart to form hydrogen atoms, the hydrogen atoms have slightly less mass than the helium atoms that split apart to make them
c
When helium atoms split apart to form hydrogen atoms, the hydrogen atoms have slightly more mass than the helium atoms that split apart to make them
d
When hydrogen atoms merge to form helium atoms, the helium atoms have slightly more mass than the hydrogen atoms that combined to make them