Concept:The Waziri served as the chief administrator and judge in the Sokoto Caliphate.Explanation:The Caliph was the overall political and spiritual head of the Caliphate.Emirs governed the various emirates under the Caliph.Imams were religious prayer leaders.The Waziri acted as the Caliph's vizier or prime minister.His key duties were the day-to-day administration of the state and the execution of justice.Therefore, the leader responsible for administration and justice was the Waziri.Answer:A. Waziri