Explanation:

• Nuclear Fusion is defined as the combining of two lighter nuclei into a heavier one.

• Such nuclear fusion reactions are the source of energy in the Sun and other stars.

• It takes considerable energy to force the nuclei to fuse. The conditions needed for this process are extreme – millions of degrees of temperature and millions of pascals of pressure.

• The hydrogen bomb is based on a thermonuclear fusion reaction. However, a nuclear bomb based on the fission of uranium or plutonium is placed at the core of the hydrogen bomb to provide initial energy.

Hence only statement 1st is correct.