You have correctly identified that m-nitrophenol should be the weakest acid among the isomers as the resulting anion cannot be stabilised by the $\text{-M}$ effect of nitro group owing to its meta location.
The acidity order of the remaining two nitrophenols can be explained in this way:
Hydr...
@Abcd ok, I had got 1>2>4>3 but that isn't even in the options. What's the right answer?
@Koolman rings of size eight or more can show stereoisomerism about an internal pi bond; that pi bond you see up top, it can be in cis and trans both forms ;)
You have correctly identified that m-nitrophenol should be the weakest acid among the isomers as the resulting anion cannot be stabilised by the $\text{-M}$ effect of nitro group owing to its meta location.
The acidity order of the remaining two nitrophenols can be explained in this way:
Hydr...
