# What is the order of acidic strength among phenol, catechol, resorcinol and hydroquinone?

This question is from a book that gives the answer as

$$\text{hydroquinone} < \text{resorcinol} < \text{phenol} < \text{catechol}$$

but does not provide any explanation for the answer. If I go by the stability of the conjugate base due to resonance, phenol seems to have the most number of resonance intermediates and seems to be most stable. Considerations about number of resonance intermediates of conjugate base gives an order that is nowhere close to that provided as an answers.

Please provide an explanation as to the provided answer or, if the answer is wrong, please supply the correct order with explanation.

Taking these factors into account, it is easy to see why hydroquinone is least acidic. Hydrogen bonding and the vicinity of the $\ce{-OH}$ to the anion (for the stronger -I effect) make cactechol more aciic than the phenol despite its +M contribution. Resorcinol has only -I effect and no counteracting electron-donating effects, which makes it the most acidic.