Chlorine has seven electrons in its valence shell. it accepts an electron to complete its octet and becomes a chlorine ion ( what is the nature of this chlorine ion? a. cation b. anion c. metal ion

The correct answer here is B - when chlorine accepts an electron to complete its octet and becomes a chlorion ion it becomes an Anion. An anion is a negatively charged ion. Chloride ions are an important electrolyte within the body.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.