Arrange the following compounds in increasing order of their acid strength.
Propan-1-ol, 2, 4, 6-trinitrophenol, 3-nitro-phenol, 3, 5-dinitrophenol, phenol, 4-methyl phenol.

When any phenol loses its acidic proton, it forms an oxygen with three lone pairs. In phenol, these lone pairs can be dislocated over the aromatic ring, providing resonance stability. This added stability allows for the easier dissociation of phenols. Thus, order of acidity is ,