What does below chemistry rebus means?

A man dies of old age on his 25 birthday. How is this possible?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

Who always enjoys poor health?

Most people think of me as money. But when they find me in the water, they won’t get any money out of me. What am I?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?

500 women soldiers are arranged in an array of ten rows and fifty columns in accordance with their respective heights. Now, the tallest woman from each row is asked to move out in the front. From them, the shortest one is labelled as Alpha. They are then asked to resume their original position.

Now, the shortest woman in each column is asked to come out in front. The tallest among them is labelled as Beta.

Can you find out if Alpha will be taller or Beta?

Jigsaw captured 100 people and make them stand in a circle and all these people are labelled as Person1, Person2, Person3... Person100. He made them play a crazy game in which Person 1 shot Person 2 and pass the gun to the next person and so on until one stands alive.

Which person will survive in the end?