Question

O- hydroxybenzoic acid is stronger than O- methyl oxy benzoic acid. Why?

Answer 1

Lets start with some information we know so far : OH- has +R and weak -I effect and we know that -I is distant dependent and +R don't Show any effect at meta position and to your note ortho substituted benzoic acids are stronger acids than benzoic acids regardless of the nature of the substituent ( be it electron donating or electron withdrawing ) due to stearic and electronic reasons.

Let's start solving :

So blindly ortho would be most acidic ( due to ortho effect as explained earlier ) now although you didn't asked but i found it quite important to share so what happens at meta is bit deep than comparing at other positions , like I told you that Oh has +R and -I and at meta +R won't show its effect so only -I left which again helps in dispersing the negative charge in other words it is more acidic than benzoic acid but less acidic than ortho one., and finally at para position -I due to its distance dependence is very weak and +R is quite strong so para is least acidic as +R intensifies negative charge.

Result : ortho hydroxy B.acid > meta hydroxy B.acid > benzoic acid > para hydroxy B. acids.

So Answer to your question should be ,

Para is least acidic.