How many sides does a circle have?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

The more of this there is, the less you see. What is it?

The dirtier I get, the whiter I look. Who am I?

I’m light as a feather, yet the strongest person can’t hold me for five minutes. What am I?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

Three ants are going up a hill, one behind the other. The last ant then says to the other ants, 'There is an ant behind me!'' How come?

What month of the year has 28 days?

I have no life, but I can die. What am I?