Answer: a red giant
Explanation:
When a sun-like star having average mass runs out of fuel-hydrogen, its atmosphere expands and the star becomes a red-giant star. The star would leave the main-sequence stage and enter the red-giant stage in which the pressure of the core is high which pushes the atmosphere outwards and thus the star expands. The pressure also leads to fusion of higher nuclei. The end stage of such a star would be formation of a white dwarf. A heavier star becomes a super-giant, goes supernova and forms a neutron star or a black-hole.
