Which form includes variations of a melody presented as a single entity?

The form described in the question, which includes variations of a melody presented as a single entity, aligns correctly with heterophony. In heterophonic music, a single melodic line is embellished or ornamented in various ways by different voices or instruments performing simultaneously. This creates a rich texture where distinct variations of the same melody coexist, reflecting individual interpretations or improvisations of the core theme.

In contrast, binary form and ternary form refer to specific structural frameworks for organizing music, focusing on the arrangement of contrasting sections rather than variations of a single melody. Monophony, on the other hand, consists solely of one melody without any accompaniment or variation. Thus, heterophony is the only choice that accurately captures the concept of presenting variations of a melody as a collective entity.