Final answer:
The average rate of decomposition of H₃PO₄ cannot be determined without specific data for its concentration over the given time period. The provided examples do not relate to H₃PO₄ decomposition rates.
Step-by-step explanation:
The average rate of decomposition of H₃PO₄ between 10.0 and 40.0 seconds cannot be calculated from the given information because there are neither specific concentration data for H₃PO₄ nor a reaction equation provided.
Normally, to calculate the average rate of a reaction, you would use the change in concentration over a specific time period. For a hypothetical reaction with data, the calculation would be Δ[Reactant]/Δt where Δ represents a change, [Reactant] is the concentration of the reactant, and t is time.
The provided exercises and examples relating to the decomposition of HO₂ and H₂O₂ as well as other reactions do not directly pertain to H₃PO₄ and therefore cannot be used to answer the original question about the average rate of decomposition of H₃PO₄.