Final answer:
The question describes a single displacement reaction where 'P' and 'R' serve as cations and 'Q' is an anion, but the options provided contain a typographical error which does not properly classify the entities as cations or anions.
Step-by-step explanation:
The question presents a single displacement reaction, which is a type of chemical reaction where one element replaces another element in a compound. The given reaction formula is PQ + R → PR + Q. In this reaction, if we assume 'P' is a cation and 'Q' is an anion, 'R' would likely be a cation looking to displace 'Q' to form 'PR'. Thus, 'P' and 'R' are cations, and 'Q' is an anion. Since there is no option combining both 'P' and 'R' are cations, and 'Q' is an anion in the choices provided, it seems there is a typographical error in the question. Typically, in a single displacement reaction, an ion in solution (often a cation) is displaced through oxidation of a metal.
An example of a single-displacement reaction is when zinc metal is placed in a solution of hydrochloric acid (HCl). The zinc replaces the hydrogen cations (H+) in the acid to form zinc chloride (ZnCl2) and hydrogen gas (H2).