Answer: Option (a) is the correct answer.
Explanation:
Elements of group 17 are known as halogens whereas elements of group 18 are known as noble gases.
Noble gases have completely filled valence shell. Therefore, they are stable and does not react easily.
Whereas halogens have incompletely filled sub-shells, therefore, in order to gain stability they react readily with another atom.
Halogen atoms are also electronegative in nature. On moving down the group, the electronegativity decreases. Thus, the atom at the top of group 17, that is, fluorine is the most reactive non-metal because fluorine has high electronegativity so, it readily attracts an electron in order to completely fill its sub-shell.
Thus, we can conclude that at the top of group 17 most reactive nonmetal elements are found on the periodic table.
