In Flourine-19, you can determine that the number of Neutrons is 10.
Now, if you look at Neon-20, you subtract its mass by the number of protons, leaving you with 10.
Therefore, Neon-20 has the same number of neutrons as Flourine-19.
The top of a wave is called the wave crest.
Where's the list? It depends on which one it is. It could be Chlorine, silicon, or anything on the non metals side of the periodic table if you don't list it.
