In the following reaction, the major products [A] and [B], respective…

The correct answer is Option (1) → [A] = p-bromophenol [B] 2,4,6-tribromophenol

The –OH group of phenol is strongly activating and ortho/para directing: its lone pair pushes electron density into the ring by resonance. So phenol undergoes bromination even without a Lewis acid, and the solvent decides how far the reaction goes:

• Br₂ in a non-polar solvent (CS₂ or CHCl₃) at low temperature (273 K): phenol hardly ionises, and the \( \ce{Br2} \) molecule is only weakly polarised. The reaction is mild and gives monobromophenols, mainly the para isomer (the ortho positions are more hindered).

      \( \displaystyle \ce{C6H5OH} \xrightarrow[\text{273 K}]{\ce{Br2}\text{ in }\ce{CS2}} \text{p-bromophenol (major)} + \text{o-bromophenol (minor)} + \ce{HBr} \)

• Bromine water: in water, phenol partly ionises to the phenoxide ion, which is even more strongly activated, and water polarises \( \ce{Br2} \). All three ortho and para positions are substituted at once, giving a white precipitate of 2,4,6-tribromophenol.

      \( \displaystyle \ce{C6H5OH + 3Br2} \xrightarrow{\ce{H2O}} \ce{C6H2Br3OH v + 3HBr} \)

In the given scheme, A is formed with \( \ce{Br2} \) in \( \ce{CS2} \) at 273 K and B with \( \ce{3Br2} \)/\( \ce{H2O} \). So A is p-bromophenol and B is 2,4,6-tribromophenol.

Why the other options are incorrect

• Option (2) [B] = o-bromophenol [A] 2,4,6-tribromophenol — Incorrect. Tribromination needs the strong activation available in water, not the milder conditions in \( \ce{CS2} \); and in water all three positions are substituted, so B cannot be a monobromo compound.

• Option (3) [A] = p-bromophenol [B] o-bromophenol — Incorrect. A is right, but in bromine water all three ortho and para positions are substituted, so B is 2,4,6-tribromophenol, not a monobromophenol.

• Option (4) [A] = 2,4,6-tribromophenol [B] p-bromophenol — Incorrect. The two products are interchanged. Tribromination does not occur in \( \ce{CS2} \) at low temperature.

NCERT (2026-27 edition):
Halogenation

Note: The same/similar question has been asked in different years by NTA as per the details given below: