PET plastic # 1 is used in water bottles and pop bottles. Why should they be recycled but not be reused?

They should be recycled but not reused because the "repeated use increases the risk of leaching and bacterial growth." Also, recycling PET plastic "results in reduced energy consumption, lower cost, and reduced environmental impact."

Part 1: Potassium (K), and Rubidium (Rb).

Part 2: Calcium (Ca) has 20 protons and 20 electrons

Explanation:

Part 1: Elements in a same column share a great deal of propreties, in this list Potassium (K), and Rubidium (Rb) are the elements that lies in the same column as Sodium (Na).

Part 2: Calcium (Ca) has 20 protons and 20 electrons. The First information is given by the periodic table, because it is organized in a way that it shows atomic number (proton number) and atomic mass and sometimes some more information about the elements. Atoms are eletricaly neutral, so there must exist 20 electrons within Calcium's orbitals to compensate its 20 protons.

A portion of a periodic table is attached.