Answer: Option (A) is the correct answer.
Explanation:
An atom who has seven valence electrons in its ground state will have the following electronic configuration in its sub shells as 2, 7.
Thus, there will be in total 9 electrons and it is known that fluorine has atomic number 9.
Whereas sodium has 2, 8, 1 electrons in its sub-shell.
Calcium has 2, 8, 8, 2 electrons in its sub-shell and oxygen has 2, 6 electrons in its sub-shell.
Thus, we can conclude that out of the given options, fluorine is the element whose atom in the ground state has seven valence electrons.
