Question

1. how do white dwarfs compare with supergiants, in terms of temperature and luminosity?

white dwarfs are cooler and have higher luminosity than supergiants.
white dwarfs are cooler and have lower luminosity than supergiants.
white dwarfs are warmer and have higher luminosity than supergiants.
white dwarfs are warmer and have lower luminosity than supergiants.

Explanation:

On the Hertzsprung - Russell (H - R) diagram, white dwarfs are located in the lower left (hotter temperature, lower luminosity) and supergiants are in the upper right (cooler temperature, higher luminosity). So white dwarfs are warmer (higher temperature) and have lower luminosity than supergiants.

Answer:

White dwarfs are warmer and have lower luminosity than supergiants.