What does below chemistry rebus means?

Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

A man had five children. He had $100 with him to give to his children. He decided to start with the youngest child and then give $2 more than each younger child to his next elder child.

For example, if he gives $x to the youngest child, he will give $(x+2) to the next one, $[(x+2) + 2] to the next one and so on.

Can you find out how much did the youngest one receive?

Your mother’s brother’s only brother-in-law is asleep on your couch. Who is asleep on your couch?

Can you find the key in the picture below?

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

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

You have a roll of cloth 1km long. You have a machine which cuts this roll into pieces of 10-meter-long cloth.

How long would it take for the machine to cut the roll if each cut took 4 secs?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99