pKa is a measure of the acidity of a particular molecule. It measures the strength of an acid by how tightly a proton is held by a Bronsted acid. The lower the value of pKa, the stronger the acid and the greater its ability to donate its protons. describe the acidity of a particular molecule.
pKa=−logKa
Hence, Assertion is true,
Phenol is more acidic than ethanol because after losing a proton (H+), phenol forms phenoxide ion which is stabilised by resonance whereas ethoxide ion is not.