How long does it take for the moon to rotate once on its axis?

27 days. You should really look that up you know ;P

Because of the moon's rotational period and orbital period are both about 28 days, it deceivingly appears that the moon never rotates. This is the result of the Earth's gravity creating "tidal bulges" on the moon which maintain this slow rotation.

What does that mean you dum bum

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.