What does this mathematical rebus means ?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

What do you get if you add 2 to 100 four times?

Can you find out the smallest number that can be conveyed as the sum of three squares in three unique ways?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

What always comes into a house through the keyhole?

Suppose you are sitting in an interview and the interviewee asks you an aptitude question.

You have three buckets with a capacity of 4 litres, 8 litres and 10 litres and you have a large tank of water. Now you have to measure 3 litres of water precisely using those buckets. How will you do it?

I have 50 feet long of cloth, I need to create 50 handkerchiefs each size of 1 foot. I take one minute to cut a 1-foot handkerchief. So how long will it take to cut 50 handkerchiefs?

What has 13 hearts but no other organs?