Which is amphiprotic? (A) H₂SO₄ (B) NH₄⁺ (C) HCO₃⁻ (D) SO₄²⁻ - HSC - SSCE Chemistry - Question 6 - 2002 - Paper 1

An amphiprotic substance is one that can act as both an acid and a base. In this case, we need to evaluate each option:

• H₂SO₄: This is a strong acid and can only donate protons, so it is not amphiprotic.
• NH₄⁺: This is a weak acid (can donate a proton) but cannot accept a proton in a manner that would define it as amphiprotic.
• HCO₃⁻: This species can both donate a proton to form CO₃²⁻ (acting as a base) and accept a proton to form H₂CO₃ (acting as an acid), making it amphiprotic.
• SO₄²⁻: This ion can only accept protons; thus, it doesn’t fit the definition of amphiprotic.

Based on this analysis, the only amphiprotic species among the options is HCO₃⁻.