Alcohols Phenols And Ethers

The pK value refers to the acidity of a substance; the lower the pK , the stronger the acid. In general, the electron-withdrawing groups such as nitro groups reduce the electron density around the hydroxyl group in phenols, making them more acidic. However, the position of the nitro group matters. The electron-withdrawing nitro group at the ortho position has a lesser effect on the hydroxy group’s acidity than the meta and para positions. Therefore, 2-nitrophenol (ortho position) has the highest pK value among the options. Thus, the correct answer is option (2) 2-Nitrophenol.