Tell me why

Little children are always curious about the things happening in their surrounding, it may be simple or complex they keep questiong their parents untill they are satisfied with the answers to their questions. This will make child to urge knowldge. Here are some sample questions with explanations which will arise on kids mind.

How do the chick come out of the egg?
What is Ozone layer ?
Why do we say "hello" while answering telephone calls?
Why does an apple float and pear sink?
Why cutting of nails and hair are painless?