It's A. volume
Pressure =

with const depends on the chosen unit of volume
I think so...
In comparison see it is very easy in goolge
Energy Levels of Electrons. As you may remember from chemistry, an atom consists of electrons orbiting around a nucleus. ... They are restricted to orbits with only certain energies. Electrons can jump from one energy level to another, but they can never have orbits with energies other than the allowed energy levels.
because it a essential for good heat transfer
-Cloudy
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