Final answer:
Emission nebulae glow red because they are ionized by hot stars, emitting their own light, while reflection nebulae reflect the light of cooler stars, often appearing blue due to light scattering effects.
Correct option is B
Step-by-step explanation:
The difference between emission and reflection nebulae primarily lies in the source of light illuminating them. Emission nebulae are clouds of ionized gas that emit light because they are energized by nearby hot stars, typically those with temperatures greater than 25,000 K. These stars emit large amounts of ultraviolet radiation that ionize the surrounding hydrogen gas, leading to the characteristic glow of emission nebulae, often seen as red due to the hydrogen alpha spectral line.
On the other hand, reflection nebulae do not produce their own light but reflect the light of nearby, cooler stars. As a result, reflection nebulae often appear blue due to the scattering effect of dust, which favors shorter wavelengths of light.