What does below chemistry rebus means?

What can you see in the middle of March and April that you can never see in any other month?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

Which is faster, Heat or Cold ? Explain.

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

In a rainy season, one day 3 huge ladies walked under a normal-sized umbrella.
The umbrella is not huge enough to accommodate all 3 ladies yet not a single lady got wet. Why?

The measurement of time, That can't be found on a clock, But can be looked upon on a map.

Who is He ?

You are given four results as below:
1111 = F
2222 = E
3333 = T
Then, can you find out how to code 4444?

I am the beginning of everything, the end of everywhere. I'm the beginning of eternity, the end of time and space. What am I?

What does below pictogram mean?