Explanation

Urotropine, also known as hexamethylenetetramine or methenamine, is an antiseptic agent. It is formed by the reaction of formaldehyde with ammonia. Formaldehyde (CHOH) reacts with ammonia (NH3) to form hexamethylenetetramine (C6H12N4), commonly represented as (CH2)6N4. This compound, urotropine, is known for its antiseptic properties and is used in various medical applications. So, the correct choice is option C. Formaldehyde.