Answer:
Hund's rule
Explanation:
Hund's rule states that for an atom in the ground state, the number of unpaired electrons is the maximum possible and these unpaired electrons have the same spin.
I will clearly illustrate this using the ground state of the nitrogen atom. Nitrogen atom contains seven electrons. Its electronic configuration is; 1s2 2s2 2px1 2py1 2pz1.
Notice that the number of unpaired electrons in this configuration is maximum and they are all expected to possess the same spin in accordance with Hund's rule
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We know because of DNA testing in general.
Density is mass divided by volume. Therefore, volume is mass divided by density.

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the particles of solids move but very slowly.
the particles of liquids move moderately fast
the particles of gas move very fast.
The reasons for this movement is the space the particles are together. Since there is not move space between solids, the particles move slowly, water there is moderate space, and air there is a lot of space.