Explanation of why fused H3PO4 conducts electricity very well:

Presence of ions:
- When H3PO4 is fused, it dissociates into H+ and H2PO4- ions.
- These ions are free to move and carry charge, facilitating the conduction of electricity.

High ion concentration:
- Fused H3PO4 has a high concentration of ions due to its dissociation.
- The abundance of charged particles enhances the conductivity of the solution.

Ability to carry charge:
- H+ and H2PO4- ions can carry electric charge through the solution.
- This movement of ions results in the flow of electricity.

Enhanced mobility of ions:
- In the molten state, ions have higher mobility compared to in the solid state.
- The increased mobility allows for better conduction of electricity.

Overall conductivity:
- The combination of ion presence, high concentration, charge-carrying ability, and enhanced mobility results in fused H3PO4 exhibiting excellent conductivity of electricity.
In conclusion, fused H3PO4 conducts electricity very well due to the presence of ions, high ion concentration, ability to carry charge, enhanced mobility of ions in the molten state, and overall conductivity characteristics.