Lewis Acid-Base Reaction in NH3 + HCl

Steps:

• Identify the reaction: NH3 (base) accepts H+ from HCl (acid) to form NH4+.
• Recall Lewis definition: Base donates lone pair to acid's empty orbital.
• Analyze each option for accuracy in describing the reaction or species.
• Select the statement aligning with electron donation in the mechanism.

Why D is correct:

• In Lewis theory, ammonia acts as a base by donating its lone pair from the nitrogen atom to the proton of HCl, forming a coordinate bond in NH4+.

Why the others are wrong:

• A: NH4+ is acidic, as it donates H+ in water (e.g., NH4+ + H2O ⇌ NH3 + H3O+).
• B: NH3 has 107° H-N-H angle (lone pair repulsion); NH4+ has 109.5° (tetrahedral).
• C: NH4+ H-N-H angle is 109.5°, matching CH4's H-C-H, but question asks for correct statement overall, not just this similarity.

Final answer: D