1. How much brighter are Red Giants than the Sun? A. 100 times; B. 1,000,000 times; C. 2 times; D. 10 times.

Also,
2. How much brighter are supergiants than giants? A. 100 times; B. 1,000 times; C. 10 times; D. the same brightness.

1. A.
Giant stars have luminosities between 10 and 1,000 times that of the Sun.

2. B.
Supergiants can have brightness from 30,000 up to hundreds of thousands times the solar luminosity.

I don't think they are brighter, they are just bigger. As our Sun becomes a red giant, the surface of the Sun will come closer and closer to us, perhaps enveloping us, so to us it gets brighter and brighter till we're burned to a cinder but that's only because we'll be closer and closer.

1. Red giants are about 100 times brighter than the Sun so A is the answer
2. Super giants are about 100 times brighter than the red giants so A is the answer

D. Although the temperature is much less the daimeter is much larger leading to a luminosity increase of around 10 times.