What does below chemistry rebus means?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

I have eight fingers and two thumbs but I do not live. What Am I?

If 21x = 79x, what is the value of x?

How many people must be gathered together in a room, before you can be certain that there is a greater than 50/50 chance that at least two of them have the same birthday?

How can you drop a raw egg from a height onto a concrete floor without cracking it?

John and Jacob are planning on a vacation. John says, "It will be better if we take the train to the hotel. We will reach faster."
To this, Jacob says, "No. You are wrong. The train stops halfway to the hotel and then we will have to walk the rest of the way. We should take the bikes to the hotel directly."
John says, "You are wrong."

Now, John takes the train while Jacob takes the bike. The train travels at four times the speed of the bike. The bike travels at twice the speed of walking.

Who do you think will reach the hotel first?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

Count the number of squares in the picture below.

The below given figure comprises of a pattern through which you can determine the missing letter. Can you push your mind to find the pattern and add the missing letter?