Properties of the ammonium ion, NH₄⁺

Steps:

• Identify NH₄⁺ structure: nitrogen atom with four hydrogens, positively charged.
• Recall hybridization: sp³, leading to tetrahedral geometry with 109.5° bond angles.
• Note bond equivalence: all four N-H bonds identical due to symmetry.
• Eliminate incorrect options by checking acid-base behavior, reactions, and shape.

Why D is correct:

• In NH₄⁺, the four N-H bonds are identical due to sp³ hybridization and tetrahedral symmetry, making them equivalent in length and strength.

Why the others are wrong:

• A: NH₄⁺ acts as a weak Brønsted-Lowry acid (NH₄⁺ ⇌ NH₃ + H⁺), not a base.
• B: Aqueous ammonium sulfate + dilute HCl forms additional ammonium salts like NH₄Cl, without producing ammonia gas.
• C: NH₄⁺ has tetrahedral shape with 109.5° bond angles; pyramidal shape (107°) describes neutral NH₃.

Final answer: D