What does below chemistry rebus means?

What animal walks on four legs in the morning, two legs during the day, and three legs in the evening?

Oedipus, the king of Thebes, figured out the answer to the riddle:

A chicken farmer has figured out that a hen and a half can lay an egg and a half in a day and a half. How many hens does the farmer need to produce one dozen eggs in six days?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

Use the digits from 1 up to 9 and make 100.

Follow the rules.
=> Each digit should be used only once.
=> You can only use addition.
=> For making a number, two single digits can be combined (for example, 4 and 2 can be combined to form 42 or 24)
=> A fraction can also be made by combining the two single digits (for example, 4 and 2 can be combined to form 4/2 or 2/4)

Question: how can we do this?

Two Twins Jack and Jill were standing back to back and suddenly they started running in opposite direction for 4 kilometres and then turn to left and run for another 3 kilometres.

what is the distance between the Baggio twins when they stop ?

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?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

Which alphabet letter is a question?