Arrange the following in increasing order of base strength in the gas phase:

(C₂H₅)₃N, C₂H₅NH₂, (C₂H₅)₂NH

(C₂H₅)₃N > (C₂H₅)₂NH > C₂H₅NH₂

According to the Lewis concept, the groups that donate electron density behave as the base. Alkylamines are basic in nature because there is a Nitrogen atom having a pair of electrons so that it can donate their electron density. As +I effect increases, the basic property of alkylamine increases, that's why in gaseous phase order of basic property of 1°, 2° and 3° ethylamine is as follows-

(C₂H₅)₃N > (C₂H₅)₂NH > C₂H₅NH₂ {Gaseous phase}

N(C₂H₅)₃ (due to inductive effect, here 3 ethyl groups are donating electrons to Nitrogen atom)

NH(C₂H₅)₂ (due to inductive effect, here 2 ethyl groups are donating electrons to Nitrogen atom)

C₂H₅NH₂ (Here in this case only 1 ethyl group is donating electrons to Nitrogen Atom)