What will happen if a low massive main sequence star runs out of hydrogen fuel?

Low mass stars are: hydrogen burning in the core while on the Main Sequence. As the hydrogen fuel runs out, extreme pressure raises the temperature to 100 million degrees, where helium burning becomes possible.

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it

because if the tool that you are using is not balanced it there would be false mass.