Question

which of the following are luminous?
campfire, star, sun
paper, rainbows, stars
candle flame, humans

Explanation:

Luminous objects are those that emit their own light. A campfire emits light due to combustion. Stars (including the Sun) are luminous as they generate light through nuclear fusion. Paper reflects light but does not emit its own. Rainbows are a reflection and refraction of light from the Sun and do not emit their own light. Humans do not emit visible light (except in some very rare biological or artificial - light - emitting cases which are not the norm here). A candle flame emits light due to the burning of wax.

Answer:

campfire, star, Sun