It is the polar nature of water that allows ionic compounds to dissolve in it. In the case of sodium chloride (NaCl) for example, the positive sodium ions (Na+) are attracted to the negative pole of the water molecule, while the negative chloride ions (Cl−) are attracted to the positive pole of the water molecule.
The answer is Strontium(Sr). The reactive increase from right to left. And this element has two valence electrons. So Rb is not correct. Then the very reactive metal is Sr.
