What does below chemistry rebus means?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

Two trains start at the same time, one from Bangalore to Mysore and the other from Mysore to Bangalore. if they arrive at their destinations one hour and four hours respectively after passing one another, how much faster is one train running than the other?

Next Number in the Series,

5, 16, 49, 104, ?

I am the fastest animal but cannot climb the tree. What am I?

By what process could you make a 'Tea-Table' into food?

No matter how little or how much you use me, you change me every month. What am I?

Remove two matchsticks to make the below equation correct.

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

The dirtier I get, the whiter I look. Who am I?