Which of the following is the conjugate base of the dihydrogen phosphate ion, H2PO4-?

• A. HPO4^{2-}
• B. H3PO4
• C. H2PO3^{-}
• D. PO4^{3-}

Answer: (A)

Verified step by step guidance

1. Recall that a conjugate base is formed when an acid loses a proton (H\textsuperscript{+}).
2. Identify the given species: the dihydrogen phosphate ion is H2PO4\textsuperscript{-}, which can act as an acid by donating one proton.
3. Remove one proton (H\textsuperscript{+}) from H2PO4\textsuperscript{-} to find its conjugate base. This means subtracting one H\textsuperscript{+} and reducing the charge by one unit.
4. Write the formula of the conjugate base after losing one proton: H2PO4\textsuperscript{-} \rightarrow HPO4\textsuperscript{2-}.
5. Compare the options given and select the species that matches the formula HPO4\textsuperscript{2-}, which is the conjugate base of H2PO4\textsuperscript{-}.