Final answer:
The Commission Plan is the municipal government form where an elected group has both executive and legislative powers, with one individual chosen as a chairperson or mayor, fitting the student's description.
Step-by-step explanation:
The form of municipal government that is being described in the student's question, where leaders are elected to supervise specific areas, used in less than 1 percent of municipalities, where one leader is chosen as chairperson or mayor, and where a group of leaders has both executive and legislative power, is best known as the Commission Plan.
Under the Commission Plan, an elected commission serves as the governing body within the municipality, performing all legislative and executive functions. This is a relatively rare form of municipal government; most municipal governments in the United States operate under a mayor-council system or a council-manager system.
By contrast, in a mayor-council system, the mayor and city council are elected separately, with the council performing legislative functions and the mayor handling executive functions. In the council-manager system, the city council appoints a city manager to carry out administrative duties, allowing the council to focus on legislative responsibilities.