Answer:
1) K and Rb
2) 20 protons, 20 neutrons, and 20 electrons.
Explanation:
1) If it's in the same column, it has the same # of valence electrons (e- on the outer shell), therefore similar chemical properties.
2)
1) atomic #, 20, is the number of protons
2) subtract the mass number from # of protons, which you get 20 neutrons
3) Number of electrons in a neutral atom = number of electrons, which is 20. You can also check yourself by looking at electron configuration on a full periodic table.
