Which stars have the highest absolute brightness?

a)supergiants
b) giants
c) yellow stars
d) dwarfs

A) Super-giants

Explanation:

Super giant star occupy the top slot in Hertzsprung-Russel diagram . They have absolute brightness between - 3 to -8. The temperature may be between 3500 K to 20000K.

28. evolution

29. environment, survive, offspring  

explanation:

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.