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.
The metal in Period 5 which is very reactive and has two valence electrons in each atom is Strontium. Hence, option (B) is correct.
Reactivity of an element is defined as the tendency to loose or gain electrons. It decreases as we move from left to right in a period and it increases as we move from up to down in a group.
A metal which belongs to Period 5 and has 2 valance electrons is Strontium. This element belongs to Group 2.
The reactivity of metals is due to the difference in stability of their electron configurations as atoms and as ions. As they are all metals they will form positive ions when they react
The outermost electronic configuration of strontium (Sr) = [Kr] 5 s²
Therefore, the correct answer is Strontium and option (B) is correct.
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