Question

Earth has atmosphere whereas moon does not have atmosphere. Justify statement.

Answer 1

It's not that the moon doesn't have an atmosphere. It has an atmosphere but it's very thin, very very thin too even be felt.

There are two main reasons for this:

The gravity on moon is very weak, its so weak that the molecules of gas do not cling firmly around the moon. So they get expelled into space even by slightest of force.The cosmic rays from the sun consists of many high energy particles that when hit the molecules of gas kicks it out into space.

So even if somehow moon develops an atmosphere around itself it won't be too long before the sun rips it off.

You can give our sun the credit for moon not having an atmosphere.

Answer 2

Earth have an atmospheric belt around it containing different layers of different densities.
whereas
Moon does not have atmosphere as it is a place of vacuum.