Final answer:
When chlorine and fluorine are covalently bonded, one pair of electrons is shared between them. This forms a single covalent bond, and a total of two electrons are shared between an atom of chlorine and an atom of fluorine.
Step-by-step explanation:
A chlorine atom needs one more electron to complete its outermost energy level, and a fluorine atom also needs one more electron to complete its outermost energy level. When chlorine and fluorine are covalently bonded, one pair of electrons is shared between them. This forms a single covalent bond. Therefore, a total of two electrons are shared between an atom of chlorine and an atom of fluorine when they are covalently bonded.