If amines are arranged in increasing order of their basic strength in gaseous phase, the correct order will be:
Inductive effect increases basicity.
NH₃ < CH₃NH₂ < (CH₃)₃N < (CH₃)₂NH
NH₃ < (CH₃)₂NH < (CH₃)₃N < CH₃NH₂
(CH₃)₃N < (CH₃)₂NH < CH₃NH₂ < NH₃
NH₃ < CH₃NH₂ < (CH₃)₂NH < (CH₃)₃N
Basicity increases with more alkyl groups due to the +I effect in gaseous phase.