Let's classify each species based on the Brønsted-Lowry acid-base theory.
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H2CO3 (Carbonic acid): This compound can donate a proton (H⁺) and acts as an acid. Therefore, it is classified as a Brønsted-Lowry acid.
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H2PO4⁻ (Dihydrogen phosphate ion): This species can both donate a proton (acting as an acid) and accept a proton (acting as a base). Therefore, it is classified as amphiprotic.
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PO4^3- (Phosphate ion): This species can accept a proton to form HPO4^2-, but does not donate a proton. Therefore, it acts only as a base in this context and is classified as a Brønsted-Lowry base.
To summarize:
- H2CO3: Brønsted-Lowry acid
- H2PO4⁻: Amphiprotic
- PO4^3-: Brønsted-Lowry base