Question

What would happen when all the hydrogen in the sun has changed into helium?

Answer 1

Then sun starts to use helium as the fuel to fuse it and it will expand to form red giant but the core shrink to give more high temprature to fuse helium. It will engulf earth's orbit while expanding

Answer 2

hey friend :-)

here is your answer

As we know that, when nuclear fusion acts on the Sun the helium gas is produced and other heavier elements up to iron(this process is known as Nucleosynthesis).

Many scientist believe that when hydrogen is used up the sun will become a big star like a dawning sun.All water on earth will be heated and convert into water vapour.
Then after some time it will become small in size and become a small white dwarf planet after some more time it will vanish and turn into small black dwarf planet.

But many scientist also believe that the product helium will also do nuclear fission and will make sun burning.

after hydrogen used up and it will become like small white dwarf plant.

hoping it helps

thanks. :D