Ammonium ion geometry

Steps:

• Identify the product: NH₃ + H⁺ forms NH₄⁺, the ammonium ion.
• Determine electron pairs: NH₄⁺ has nitrogen bonded to four hydrogens, with four bonding pairs and no lone pairs.
• Apply VSEPR theory: Four electron pairs around central atom predict tetrahedral electron geometry.
• Confirm bond angle: Tetrahedral arrangement yields 109.5° H-N-H angles.

Why D is correct:

• NH₄⁺ has tetrahedral molecular geometry with 109.5° bond angles, as VSEPR theory dictates for AX₄ notation (A = central atom, X = ligand).

Why the others are wrong:

• A describes NH₃ (pyramidal, 107° due to lone pair repulsion), not NH₄⁺.
• B incorrectly assigns tetrahedral angle to pyramidal shape.
• C mismatches tetrahedral geometry with NH₃'s 107° angle.

Final answer: D