Which of the following elements has eight valence electrons?
a. argon
b. beryllium
c. chromium
d. oxygen

Option (a) is the correct answer.

Explanation:

Atomic number of argon is 18 and its electronic configuration is  . Hence, there are eight electrons present in the outermost shell of argon.

Atomic number of beryllium is 4 and its electronic configuration is . Only 2 electrons are present in its outermost shell.

Atomic number of chromium is 24 with electronic configuration . There are only 5 valence electrons present in it.

Atomic number of oxygen is 8 and its electronic configuration is . 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.