What does below chemistry rebus means?

What does this rebus means ?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

I am a normal creature, but I have five hands. I can even have more but even then I will be considered normal.

Who am I?

I am a type of room you cannot enter or leave. Raised from the ground below, I could be poisonous or a delicious treat. What am I?

How many Watermelons are there in the below picture?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

I’m light as a feather, yet the strongest person can’t hold me for five minutes. What am I?

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.