What is so fragile that saying its name breaks it?

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?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

What word is pronounced the same if you take away four of its five letters?

What runs around the whole yard without moving?

What is at the end of a rainbow?

There are 2 cops parked along a one-way street looking for traffic violations. They spot a taxi driver going in the wrong direction, yet they do nothing.

Why?

Name the three-letter word that can complete the below words:

A) L O _ _ _ E
B) E D U _ _ _ E
C) _ _ _ E R
D) _ _ _ T L E

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

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?