According to Lewis concept, an acid is

Correct option is B

The correct answer is (b) Electron pair acceptor

• The Lewis concept, proposed by G.N. Lewis in 1923, defines acids and bases based on electron pairs rather than protons.

• A Lewis acid is a species that accepts an electron pair, while a Lewis base is one that donates an electron pair.

• This definition is broader than the Brønsted-Lowry concept and includes non-protonic acids like metal ions and electron-deficient molecules.

• Example:

  BF3+NH3→F3B←NH3\text{BF}_3 + \text{NH}_3 \rightarrow \text{F}_3\text{B} \leftarrow \text{NH}_3BF3​+NH3​→F3​B←NH3​

• Here, BF₃ (electron-deficient) is the Lewis acid, and NH₃ (donates electron pair) is the Lewis base.

Information Booster:
• Lewis Acid: Accepts an electron pair (e.g., BF₃, AlCl₃, Fe³⁺).
• Lewis Base: Donates an electron pair (e.g., NH₃, OH⁻, H₂O).
• This theory explains acid-base reactions without involving protons (H⁺).
• Useful in understanding coordination chemistry and catalysis.
• All Brønsted-Lowry acids are Lewis acids, but not all Lewis acids are Brønsted-Lowry acids.
• Molecules with vacant orbitals often act as Lewis acids.