Answer:
D. a negatively charged ion
Step-by-step explanation:
In the neutral state of any element the number of electrons and number of protons are equal in the number. Here in this case since number of electrons are 15 ( equal to atomic number) therefore number of protons are also 15. When 3 electrons are gained by the element this results in a a negatively charged ion. The ion will have -3 charge over it. It either means excess of three electrons or deficiency of three protons.