What was observed that led to the arrangement of sixty-three already known elements by increasing atomic weights in the periodic table?

Ions gain or lose electrons

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium

Molarity is moles of solute over liters of solution. idk if that is what you are talking about, but you can convert moles of solute to grams of solute using dimensional analyzes by using molar mass found on the periodic table.