What is at the end of a rainbow?

I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?

Living above a star, I do not burn
Eleven friends and they do not turn
I can just be visited in a sequence, not once or repeatedly
PQRS are my initials
Can you tell my name accurately?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

What has 88 keys?

Can anyone tell me a word in the English dictionary which has a silent 'z'?

What is always in front of you but can’t be seen?

If you’ve got me, you want to share me; if you share me, you haven’t kept me. What am I?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?