Answer: The correct answer is oxygen.
Explanation:
Reactivity is defined as the tendency of an atom to loose or gain electrons.
The reactivity of non-metal increases as we move from left to right in a period and decreases as we move from top to bottom in a group.
The given elements are non-metals as they belong to group 15 and group 16 of the periodic table.
For the given options:
Nitrogen (N): It belongs to Group 15 and Period 2 of the periodic table.
Oxygen (O): It belongs to Group 16 and Period 2 of the periodic table.
Selenium (Se): It belongs to Group 16 and Period 4 of the periodic table.
Sulfur (S): It belongs to Group 16 and Period 3 of the periodic table.
From the given elements, the most reactive element will be oxygen.
Order of reactivity of metals follows:
[tex]\text{Oxygen}>\text{Nitrogen}>\text{Sulfur}>\text{Selenium}[/tex]
Hence, the correct answer is oxygen.
