Final answer:
Al³⁺ is an ion, specifically a cation with a 3+ charge created when an aluminum atom loses three electrons.
Step-by-step explanation:
The subject in question, Al³⁺, is b) An ion. Specifically, it is a positively charged ion, or a cation. This occurs when an atom of aluminum loses three electrons and gains a net positive charge. To elaborate, since the number of protons in an atom determines its elemental identity and this number remains constant, an aluminum atom has 13 protons. When it becomes an ion with a 3+ charge (Al³⁺), it means it has lost three electrons, thus having 10 electrons instead of its usual 13, creating an imbalance in charge. Therefore, Al³⁺ is an ion with a 3+ charge due to the loss of three electrons from the neutral atom.