Which uniform item is worn to denote a soldier's rank?

The correct answer, insignia, is worn on the uniform to signify a soldier's rank within the Army. Insignia includes rank insignia that is typically displayed on the shoulders or collar of the uniform, clearly indicating the soldier's position and level of authority. This visual representation is crucial for maintaining the chain of command and ensuring that all personnel can quickly and easily recognize the rank of individuals in uniform.

While patches may refer to other distinguishing features or unit affiliation, they do not specifically denote rank. The belt buckle and suspenders, while they might be part of the uniform, do not serve the purpose of indicating a soldier's rank. Instead, insignia provides a standardized and recognized means of displaying rank throughout the Army, which is essential for proper military functioning and discipline.