The strongest acid from the following is

CONCEPT:

Acidity and Electron-Withdrawing Groups (EWG)

• Acidity of compounds is influenced by the ability of substituents on the aromatic ring to either donate or withdraw electron density.
• Electron-Withdrawing Groups (EWGs), such as -NO₂, -CN, -COOH, etc., decrease the electron density on the ring, making the hydrogen more likely to dissociate as a proton (H⁺), which increases the acidity of the compound.
• In contrast, Electron-Donating Groups (EDGs), such as -CH₃, -OH, -OCH₃, increase the electron density on the ring, making the hydrogen less likely to dissociate, thus decreasing the acidity.

EXPLANATION:

• In the given compounds:

  The compound with -NO₂ (Nitro group) is the strongest acid among the options.

  • 
  • The -NO₂ group is a strong electron-withdrawing group (EWG), which pulls electron density away from the ring, making the hydrogen on the hydroxyl group (OH) more acidic.
  • The -OH group in the presence of -NO₂ becomes more likely to release a proton (H⁺), increasing the acidity.
• The -Cl (Chlorine) and -CH₃ (Methyl) groups are less electron-withdrawing, and thus, they do not increase the acidity as much as -NO₂.
• The -OH group attached to the benzene ring with an electron-donating group like -CH₃ decreases the ring's ability to lose a proton, thereby reducing acidity.

Therefore, the strongest acid from the following compounds is the one with the -NO₂ group attached to the benzene ring.