Types of Sets

A set is classified as a singleton set when it contains exactly one distinct element. In H = {12}, the braces indicate that 12 is an element of H, and there are no other elements listed. Therefore, the cardinality of H is |H| = 1, which satisfies the definition of a singleton set. It is not an empty set because an empty set contains no element and is written as ∅ or { }. It is not infinite because it has only one element. “Equal set” is not the appropriate classification here; equality describes a relationship between two sets that have exactly the same elements. Thus option A is correct.