What does below chemistry rebus means?

Replace the question mark with the correct number.

When it is alive we sing, when it is dead we clap our hands. What is it?

On one occasion, A Boy collects 71 rupees in form of 20 paise and 25 paise. He collects a total of 324 coins.

Can you tell me how many 20-paisa and 25-paisa he got?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

You can hear me, but you can't touch or see me.

What am I?

Four children having five rocks each were playing a game in which they had to throw the rock at a particular solid area in the water. Child 1- Succeeded in throwing three rocks at a solid area but one of the rocks sunk. Child 3 - His aim was so bad that all rocks got sunk. Child 4- He was awesome and none of the rocks got sunk. Child 2 - Was the winner but was struck by a rock in the head and died. Who killed Child 2?

Can you start the fire using two pieces of wood?

Remove two matchsticks to make the below equation correct.

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M