Which of the following is the chemical formula for the oxyacid perphosphoric acid?

• A. H3PO3
• B. H4P2O7
• C. H3PO4
• D. H3PO5

Answer: (D)

Verified step by step guidance

1. Understand that an oxyacid consists of hydrogen, oxygen, and another element (in this case, phosphorus). The name 'perphosphoric acid' suggests it is a phosphorus oxyacid with the highest number of oxygen atoms compared to other related acids.
2. Recall common phosphorus oxyacids and their formulas: phosphorous acid (H3PO3), pyrophosphoric acid (H4P2O7), and phosphoric acid (H3PO4). These have fewer oxygen atoms than the 'per' form.
3. Recognize that the prefix 'per-' in oxyacids typically indicates the acid with the maximum number of oxygen atoms bonded to the central atom, which is more than in phosphoric acid (H3PO4).
4. Use the general pattern for naming oxyacids: the 'per-' prefix corresponds to an acid with one more oxygen atom than the 'ic' acid. Since phosphoric acid is H3PO4, perphosphoric acid should have one more oxygen, making it H3PO5.
5. Confirm that the formula H3PO5 matches the name perphosphoric acid, as it contains three hydrogens, one phosphorus, and five oxygens, consistent with the naming convention.