What does neutral ferric chloride test detect?

Neutral ferric chloride solution is commonly used in qualitative organic analysis to detect:

• phenolic $-OH$ group
• acetate ion

Why phenolic $-OH$?

Phenols react with neutral $\mathrm{FeCl_3}$ to give a colored complex (often violet, blue, green, etc.). This is a standard test for phenols.

Why not alcoholic $-OH$?

Ordinary alcohols do not give this characteristic ferric chloride coloration test. So alcoholic $-OH$ is not detected by neutral ferric chloride.

Why acetate ion?

Acetate ion can also react with ferric ions to give characteristic coloration/complex formation, so neutral ferric chloride is used for its detection as well.

Check each option:

• A: sulphide ion and alcoholic $-OH$ group
  Incorrect, because alcoholic $-OH$ is not detected by neutral ferric chloride.

• B: acetate ion and phenolic $-OH$ group
  Correct, because both are detected using neutral ferric chloride.

• C: sulphide ion and phenolic $-OH$ group
  Incorrect, because sulphide ion is not the standard identification here.

• D: acetate ion and alcoholic $-OH$ group
  Incorrect, because alcoholic $-OH$ is not detected.

Final answer

The reagent neutral ferric chloride is used to detect the presence of acetate ion and phenolic $-OH$ group.