The most acidic compound among the following is:

The acidity of phenols depends on the stability of the phenoxide ion formed after the loss of a proton. Electron-withdrawing groups (EWG) such as the nitro group (-NO₂) stabilize the phenoxide ion through resonance (-R effect) and inductive (-I effect) effects, thereby increasing acidity. This effect is most pronounced when the EWG is at the ortho or para position. Conversely, electron-donating groups (like alkyl groups) destabilize the phenoxide ion and decrease acidity. Although the specific structures are missing from the input, in the context of NEET exams, 'Option 1' often refers to a compound with multiple electron-withdrawing groups, such as 2,4,6-Trinitrophenol (Picric acid), or a specific isomer like p-Nitrophenol, which are significantly more acidic than phenol or cresols. (See NCERT Class 12, Unit 11, Section on Acidity of Phenols; Principles of resonance and inductive effects are discussed in NCERT Class 11, Unit 12, Sections 12.7.5 and 12.7.6).