Give reason : Inert gas shows least reactivity
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Noble gases also known as inert gases are the least reactive of all known elements because with eight valence electrons, their outer energy levels are full. As a result, noble gases cannot become more stable by reacting with other elements and gaining or losing valence electrons. Therefore, noble gases are rarely involved in chemical reactions and almost never form compounds with other elements.

Explanation:

The only exception is helium, which has just two electrons. But helium also has a full outer energy level, because its only energy level (energy level 1) can hold a maximum of two electrons. A full outer energy level is the most stable arrangement of electrons.

it's c. elements are placed in rows based on how may valencies electrons have.