What is atmosphere ?

Why can't we see air ?

What would have happened if there would have been no atmosphere around the earth ?

What do you observe when

(a) Ice cold water is filled in a glass tumbler.

(b) A burning candle is covered with an inverted jar.

(c) Carbon dioxide gas is passed through lime water.

(d) A beam of light is allowed to enter in a closed dark room through a small hole.