Which metal in period 5 is very reactive and has two valence electrons in each atom? rubidium (rb) strontium (sr) zirconium (zr) silver (ag)

           Strontium (Sr)

                        The condition given in statement is the presence of two valence electron. Hence, first we found the electronic configuration of given atoms as follow;

                       Rubidium                         [Kr] 5s¹

                      Strontium                        [Kr] 5s²

                       Zirconium                         [Kr] 4d² 5s²

                      Silver                                 [Kr] 4d¹⁰ 5s¹

From above configurations it is cleared that only Strontium and Zirconium has two electrons in its valence shell.

We also know that s-block elements are more reactive than transition elements due to less shielding effect in transition elements hence, making it difficult for transition metals to loose electrons as compared to s-block elements. Therefore, we can conclude that Strontium present in s-block with two valence electrons is the correct answer.

a electronegativity decreases beacuse the size of nucleus is bigger.