Answer: BF 4 - (fluoroborate anion).
- A BF<sub>4</sub><sup>-</sup> (fluoroborate anion)
- B CuF under most conditions encountered
- C NaF as frequently observed in practice
- D HF directly in many documented cases
Correct answer: A. BF<sub>4</sub><sup>-</sup> (fluoroborate anion)
Explanation: Balz-Schiemann reaction: ArN2+BF<sub>4</sub><sup>-</sup> is thermally decomposed to give the aryl fluoride (ArF).
In aniline, the nitrogen's lone pair is pulled into the benzene ring through resonance, leaving less electron density available to accept a proton - which is why aniline is a much weaker base than methylamine, where the lone pair is fully available.
Concept context
Nitrogen-containing organic compounds. Covers classification (primary, secondary, tertiary), basicity comparison, preparation methods, and reactions including diazotization and coupling, key for understanding dyes and pharmaceuticals.