Answer: Option (a) is the correct answer.
Explanation:
Atomic number of argon is 18 and its electronic configuration is \([Ne] 3s^{2}3p^{6}\). Hence, there are eight electrons present in the outermost shell of argon.
Atomic number of beryllium is 4 and its electronic configuration is \(1s^{2}2s^{2}\). Only 2 electrons are present in its outermost shell.
Atomic number of chromium is 24 with electronic configuration \([Ar] 4s^{1} 3d^{5}\). There are only 5 valence electrons present in it.
Atomic number of oxygen is 8 and its electronic configuration is \(1s^{2}2s^{2}2p^{4}\). Hence, there are only 6 electrons present in its valence shell.
Thus, we can conclude that out of the given options argon element has eight valence electrons.
