Which of the following is true about nuclear fusion and stellar life cycle?

1. Nuclear fusion has the ability to occur easily in everyday situations.

2. Nuclear fusion occurs in the core of protostar.

3. Nuclear fusion occurs in the core of a protoplanet.

4. Nuclear fusion occurs the atmosphere of a star.

The life cycle of a star begins in the nebula where it is merely composed of matter, gas and dust. As time progresses, gravitational force causes the hydrogen gas in the nebula to start to spin, With increased spinning, the constituents are heated up and forms a Protostar.

Now because of the unstable Protostar in the core of the cloud is burning at a temperature of about 15,000,000 degrees Fahrenheit, Nuclear fusion occurs. This converts the hydrogen gas to helium in the core causing the protostar to become stable and glow like a main sequence star.

Also the inner shell contracts and becomes unstable as the helium replaces hydrogen while the outer shell of the star still hydrogen dense expands outwards and cools forming a giant star.

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