Ammonia as base neutralizes carbonic acid

Steps:

• Reactants: NH3 (base), CO2 + H2O form H2CO3 (acid).
• Balanced equation: 2NH3 + CO2 + H2O → (NH4)2CO3.
• Proton transfer: NH3 accepts H+ from H2CO3, forming NH4+ and CO3^2-.
• Classify: Involves acid-base neutralization, not redox or structural change.

Why B is correct:

• Acid-base reaction defined by proton donation (H2CO3 as acid) to acceptor (NH3 as base), per Brønsted-Lowry theory.

Why the others are wrong:

• A: No change in oxidation states (N remains -3, C +4); not redox.
• C: H-N-H angle increases from 107° in NH3 to 109.5° in tetrahedral NH4+.
• D: Stoichiometric ratio is 2:1:1, not 1:1:1.

Final answer: B