Question

what are the small particles that can be seen in a beam of light that enter a dark room

Answer 1

dust particles can be seen a beam of light that enter a dark room

Answer 2

There are many dust particles present in our surroundings. Some of them can't be seen when excessive amount of light is present. So when a beam of sunlight or any other kind of light comes in the room, we can see the dust particles.

So the main answer is the small particles are nothing but dust particles.

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