Which of the following represents the correct decreasing order of basic strength for methyl substituted amines and ammonia in the gas phase?

Step-by-step solution

In the gas phase, there are no solvent molecules to stabilize the conjugate acid through hydrogen bonding (solvation effect). The basic strength of amines in the gas phase is determined solely by the electron-donating inductive effect (+I) of the alkyl groups. More alkyl groups increase the electron density on the nitrogen atom, making it a stronger base. Thus, the basicity strictly follows the order: tertiary > secondary > primary > ammonia. For methylamines, the correct decreasing order is ( CH ₃)₃ N > ( CH ₃)₂ N