The correct order of relative acidic strength of the following compouonds is

Options

A. phenol `gt`- o-nitrophenol `gt` m-nitrophenol `gt` p-nitrophenol
B. p- nitrophenol `gt` m-nitrophenol `gt`o-nitropenol `gt` phenol
C. p-nitrophenol `gt` o-nitrophenol `gt` m-nitrophenol `gt` phenol
D. o- nitrophenol `gt` m-nitrophenol `gt` p-nitrophenol `gt ` phenol

Answer

C

Explanation

Since `-NO_(2)` group is an electron withdrawing group, so it stabilises the phenoxide ion. Hence, nitriophenol is more acidic than phenol.
Again `-NO_(2)` group can enter into resonance and shows. -R-effect with the hydroxyl group both at ortho and para-position.
Hence ortho and para-nitrophenols are stronger acids than phenol. A meta-nitro group can't enter into resonance with hydroxyl group but it can exert -l-effect from this position.
So it is stronger than phenol but weaker than ortho and para-isomer. Further due to posibililty of intramolecular hydrogen bonding in o-isomer, its acidic strength is slightly weasker than para-isomer. Theri acidic strength is in the order:
`p`- nitrophenol `gt` o-nitrophenol `gt` m-nitrophenol `gt` phenol.