Some human traits are controlled by more than two alleles this is called

Human traits controlled by multiple alleles are called multiple-allele traits. One widely known example is ABO blood type, which is controlled by 3 alleles.

The two are potassium and rubidium. Why? Na is an alkali metal. As you go down the metals become more reactive. 
Calcium has 20 protons. Why? The atomic # is 20 (the one at the top).
It has 20 neutrons. Why? The atomic mass (the number on the bottom) is ~40, ignoring electron mass. 40- 20 protons = 20 neutrons. 
It has 20 electrons. 
Why? The # of protons and electrons is the same. Ions aren't on the periodic table.
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