What does below chemistry rebus means?

In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?

A girl is twice as old as her brother and half as old as her father. In 50 years, her brother will be half as old as his father. How old is the daughter now?

Why Aeroplane windows are round?

Solve the rebus riddle in the picture below.

If it took eight men ten hours to build a wall, how long would it take four men to build it?

Can you place three balls such that the equation shown in the picture holds true?

Below, you can see some coding:
January = 1017
February = 628
March = 1335
April = 145
May = 1353
June = 1064
July = 1074
August = 186

Now deciphering the way it has been coded, can you find out how September will be coded?

If you read clockwise, you can form a word by inserting three missing letters in the picture given below. Can you do it?

I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?