Concept:The event in 1953 that led to the suspension of Nigeria's constitution and the declaration of a state of emergency was the Kano riots.Explanation:In May 1953, southern politicians from the Action Group visited Kano to campaign for self-government.This visit triggered violent political and ethnic clashes between Northerners and Southerners in the city.The breakdown of order alarmed the British colonial authorities.They responded by declaring a state of emergency and suspending the Macpherson Constitution in the Northern and Western Regions.The Kano riots exposed the deep regional tensions facing Nigeria during its transition to self-rule.Answer:C. Kano riots