Which of the following order is correct?

Answer

Acid strength order: `I gt III gt II gt IV`

Explanation

Step-1: Notice that `CH_(3)` have +I effect so all methyphenols (cresols) are less acidic than phenol (I).
Step-2: Now amongst cresols P-and o-`Ch_(3)` are increasing the `e^(-)` density due to their hyper conjugation but ortho isomer has viable +I effect also, which will help in destabilising phenoxide ion therefore O- is least acidic. Since at meta position only +I works it as least `e^(-)` density amongst the cresol.