The conjugate acid of CH3NH2, which is methylamine, is CH3NH3+. This occurs when methylamine accepts a proton (H+). In the context of Brønsted-Lowry acid-base theory, an acid is defined as a proton donor, and a base is a proton acceptor. Methylamine acts as a base by accepting a proton, resulting in its conjugate acid.
To explain further, when a base (like CH3NH2) accepts a proton, it becomes its conjugate acid (CH3NH3+). This transformation is common in acid-base reactions, where the act of protonation converts a base into its corresponding conjugate acid. Therefore, if you are considering reactions involving methylamine, it is important to recognize that CH3NH3+ is its conjugate acid, which can participate in subsequent reactions as an acid itself.