c
The correct order of relative basicity of amines in the gas phase is \(3^o > 2^o > 1^o > NH_3\) The alkyl group releases electron and thus, tends to disperse the positive charge of the alkyl ammonium ion and therefore stabilises it. Since, \(NH_4^+\) (from \(NH_3\)) has no such alkyl group, it is not stabilised to such an extent as alkyl ammonium ion.