Which best describes nuclear fusion? a nucleus spontaneously splits and absorbs energy. two nuclei spontaneously combine and absorb energy. a nucleus collides with a neutron and splits, releasing energy. nuclei combine to form a heavier nucleus, releasing energy.

Answer is: Nuclei combine to form a heavier nucleus, releasing energy.

For example, fusion of hydrogen atoms at the Sun.

This fusion nuclear reaction is in the inner core of the Sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).

The inner core is the central region of the Sun and all solar energy is produced in the core by nuclear fusion.

the answer to this question is 3.