When floating a ping-pong ball with a hairdryer, which two forces are balanced?

The energy equivalent of the rest mass of an electron is

Consider an ideal gas at 27.0 degrees celsius and 1.00 atmosphere pressure. imagine the molecules to be uniformly spaced, with each molecule at the center of a small cube. what is the length l of an edge of each small cube if adjacent cubes touch but don't overlap?

Directions: count the number of atoms. ar co2 na3po4 so3 nac2h3o2