I know that a strong electron withdrawing group reduces electron density and makes a molecule more acidic. Also, a meta substituent will have less effect than ortho and para substituence and the para isomer will be more acidic than the ortho one. The point that I wonder: Does the acidity always increase with the number of withdrawing group as well?
Some group, let's say, phenol has one strong electron withdrawing group like nitro, carboxyl, chloro etc. If phenol would have two more of that same withdrawing group attached, would it be simply more acidic? Or, should another factors be considered to determine the acidity? I thought that maybe it would be more reliable to look $\mathrm{p}K_\mathrm{a}$ values but couldn't find any molecule that fits that situation.