The least reactive non metal in the given option is sulfur (S).
The electronegativity of non metals increases from left to right in the periodic table and and decreases down the group.
The most reactive non metals are found in the group 7. These non metals include the following in theirs order of reactivity;
- fluorine (F),
- chlorine (Cl),
- bromine (Br),
- iodine (I), and
- astatine (At)
Oxygen and sulfur are found in the group 6 of the periodic table, oxygen has lower atomic size and it is found above sulfur. Since the reactivity of non metals decreases down the group, oxygen is more reactive than sulfur.
Thus, the least reactive non metal in the given option is sulfur (S).
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