Which of the following is the correct decreasing order of basic strength in the gas phase?
In the gas phase, basicity increases with the number of alkyl groups due to the inductive effect: (C₂H₅)3N > (C₂H₅)2NH > C₂H₅NH₂ > NH₃ . This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Relevant Chemistry topic covering principles and examples as per NCERT.