For sun to convert into a red giant, which of the following should hold?

All the above.

This is the process of death of a star. When the hydrogen at the core of the star is completely burnt, it will start to cool off and the start begins to collapse under its own gravity. The temperature then rises again and at about 10⁸ K, fusion of helium into carbon begins. When all of the helium is burnt, then the process repeats untill carbon fuses to form other higher elements. The star then enters the phase of being a red giant as its outer envelope expands.