The correct answer is option 4: Phosphoric acid.
To understand why phosphoric acid is considered a tribasic acid, we need to understand what is meant by the term "tribasic." Tribasic refers to the number of hydrogen atoms that can be replaced by a metal or a base in a chemical reaction.
Phosphoric acid, with the chemical formula H3PO4, is composed of three hydrogen atoms (H) and one phosphate ion (PO4). Each hydrogen atom in phosphoric acid can be replaced by a metal or a base, leading to the formation of three different salts. This property of phosphoric acid makes it tribasic.
On the other hand, hydrochloric acid (option 1), nitric acid (option 2), and sulfuric acid (option 3) are not tribasic acids. Hydrochloric acid (HCl) is monobasic because it can only replace one hydrogen atom. Nitric acid (HNO3) is also monobasic. Sulfuric acid (H2SO4) is a dibasic acid because it can replace two hydrogen atoms.
Therefore, the correct answer is option 4: Phosphoric acid, which is a tribasic acid.