What does below chemistry rebus means?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

When 99 is considered higher than 100?

I was born in a small house and I live in it all alone. No windows and no doors have been assigned to my house. The only way I can go out is by breaking through the walls of my house.

Who am I?

You see me once in June, twice in November, and not at all in May. What am I?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

I look at you, you look at me I raise my right, you raise your left. What am I?

Can you identify the hidden rebus in the image below?

What building has the most stories?

I have thought of a number that is made up by using all the ten digits just once. Here are a few clues for you to guess my number:

First digits is divisible by 1.
First two digits are divisible by 2.
First three digits are divisible by 3.
First four digits are divisible by 4.
First five digits are divisible by 5.
First six digits are divisible by 6.
First seven digits are divisible by 7.
First eight digits are divisible by 8.
First nine digits are divisible by 9.
The number is divisible by 10.

Can you find out the number ?