(A) Presence of electron withdrawing groups at p-position, increases the acidic strength of phenols
(R) Presence of electron withdrawing groups at ortho and para position stabilises the phenoxide ion formed

In substituted phenols, the presence of electron withdrawing groups such as nitro group, enhances the acidic strength of
phenol. This effect is more pronounced when such a group is present at ortho and para positions. It is due to the effective
delocalisation of negative charge in phenoxide ion.