Which of the following is a monatomic cation?

A. Fr + <- - I believe this is correct.

B. NH4+

C. Br-

D. OH-

A. Fr+

Explanation:

A monatomic ion is an ion consisting of exactly one atom. If an ion contains more than one atom, even if these are of the same element, it is called a polyatomic ion. For example, calcium carbonate consists of the monatomic ion Ca²⁺ and the polyatomic ion CO₃²⁻.