Agas has a shape that conform to the container shape, but fills the entire shape and, thus form an upper surface.

varying, does, does not

Explanation:

A gas does not have a defined volume on its own. It takes up the shape of the whatever container it is in.

This is due to the fact that gasses have weak inter-molecular forces between them. Gases are generally compressible unlike liquids which are mostly incompressible. Some, example of gases are  hydrogen (H2), nitrogen (N2), oxygen (O2) etc.

it takes about 30 days for it to break down