Which of the following can behave both as a Brønsted–Lowry acid and as a Brønsted–Lowry base? (a) HCO3- (b) CN- (c) H2O (d) H2CO3

Verified step by step guidance

1. Step 1: Understand the Brønsted–Lowry acid-base theory, which defines an acid as a substance that can donate a proton (H⁺) and a base as a substance that can accept a proton.
2. Step 2: Analyze each option to determine if it can donate a proton (acting as an acid) and accept a proton (acting as a base).
3. Step 3: Consider option (a) HCO₃⁻. As an acid, it can donate a proton to form CO₃²⁻. As a base, it can accept a proton to form H₂CO₃.
4. Step 4: Consider option (b) CN⁻. It can accept a proton to form HCN, but it cannot donate a proton, so it cannot act as an acid.
5. Step 5: Consider option (c) H₂O. It can donate a proton to form OH⁻ (acting as an acid) and accept a proton to form H₃O⁺ (acting as a base).