What does below chemistry rebus means?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

What is greater than gold but cannot be bought. it can never be sold and can earn if its sought. though it can be broken, it can still be fixed. for by birth it can't start nor by death it is ended.what am i?

Can you name four days which start with the letter 'T'?

Can you find out what is missing?

1 3 5
2 4 ?

Hint: It's not six. Think out of the box.

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

Make a sentence consisting of three words that have the whole alphabet.

Find out which of the given views in the picture is accurately the top view of the given pyramid.

People are waiting in line to board a 100-seat aeroplane. Steve is the first person in the line. He gets on the plane but suddenly can't remember what his seat number is, so he picks a seat at random. After that, each person who gets on the plane sits in their assigned seat if it's available, otherwise, they will choose an open seat at random to sit in. The flight is full and you are last in line. What is the probability that you get to sit in your assigned seat?

What is the next number in this matchsticks series riddle?