The stars that are only fusing hydrogen into helium at this time are :
Characteristic of a star fusing hydrogen into helium
A star fusing hydrogen into helium is categorised as a main sequence star. As a star continues to fuse hydrogen into helium, energy is released in the process and the luminosity of the star increases as well. An example of a star that has completely fused hydrogen into helium is the sun. A giant red star signifies that the star is out of hydrogen it uses for nuclear fusion.
Hence we can conclude that the stars undergoing hydrogen fusion into helium are stars 1, 2 and 3
Learn more about main sequence stars : https://brainly.com/question/14631675
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