Like any star of similar mass would do , once the Sun has exhausted the hydrogen in its core , it expands into a red giant, eventually ejecting its outer envelope of gases to become a white dwarf
1) same
2) Like any star of similar mass , once the hydrogen the Sun's core has exhausted, then it expands into a red giant and eventually ejects
3) As in the case of any star of similar mass , once the hydrogen in the Sun's core is exhausted , it will expand into a red giant , and eventually ejecting
4) As any star of similar mass would , once the hydrogen in the Sun's core is exhausted it will expand into a red giant and will eventually eject
5) As would be the case with any star of similar mass , once the Sun exhausts the hydrogen in its core , it will expand into a red giant and eventually eject

Which one is correct. This is from Powerscore

it refers to Sun and not to Sun's core thus B and C can be eliminated

You are comparing so start with sun - "like" would prefer then "as" - B,C and D can be eliminates

A seems to be correct. - once seems awkward in A but based on reasoning above I would go with A.