Final answer:
Mg2+ is called a basic radical because it forms a strong base when combined with hydroxide ions and neutralizes acids to form salts, demonstrating properties of alkaline earth metals.
Step-by-step explanation:
The term 'basic radical' refers to a cation that, when combined with an anion, forms a basic compound. Magnesium ion, Mg2+, is called a basic radical because it readily combines with hydroxide anions (OH-) to form magnesium hydroxide, Mg(OH)2, which is a strong base. This reaction is typical of alkaline earth metals like magnesium. When the Mg2+ ion reacts with a strong acid such as hydrochloric acid (HCl), it forms an ionic bond with the Cl- anion resulting in the salt, MgCl2, and demonstrates the behavior of a basic radical in neutralizing acids and forming a base in reaction with water.