Arrange the following in the correct order of their basic character
I) NH₃
II) CH₃NH₂
III) C₆H₅NH₂

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I = II = III

II > III > I

II > I > III

III > II > I

answer is C.

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Detailed Solution

Basic strength of an amine is determined by availability of electron from nitrogen.
Due to the electron releasing nature of alkyl group, it pushes the electrons toward nitrogen and thus, makes the unshared electron pair more available for sharing with the proton of the acid.
Moreover, the substituted ammonium ion formed from the amine gets stabilized
due to dispersal of the positive charge by the +I effect of the alkyl group.
Hence, alkyl amines are stronger bases than ammonia.
In aniline or other aryl amines, the -NH₂group is attached directly to the benzene ring.
It results in the unshared electron pair on nitrogen atom to be in conjugation with the benzene ring and thus, making it less available for protonation with an acid.
Aniline is a resonance hybrid of five structures.
On the other hand, anilinium ion obtained by accepting a proton can have only two resonating structures.
Thus, aniline (five resonating structures) is more stable than anilinium ion.
Hence, the proton acceptability or the basic nature of aniline or other aromatic amines would be less than that of ammonia.
Hence, the correct order of basic strength is:
CH₃NH₂ > NH₃> C₆H₅NH₂.