Calculate the [H₃O⁺] and pH of a strong diprotic acid with pK_a2 = 2.5 ×10⁻² at the given concentrations. At which given concentration(s) does the assumption "x is negligible" not applicable?
i. 1.0 M
ii. 0.10 M
iii. 0.01 M

• A. i. [H₃O⁺] = 1.3 M; pH = 0ii. [H₃O⁺] = 0.21 M; pH = 0.68iii. [H₃O⁺] = 0.15 M; pH = 0.96x is not negligible in all of the given concentrations.
• B. i. [H₃O⁺] = 1.0 M; pH = 0ii. [H₃O⁺] = 0.10 M; pH = 1.1iii. [H₃O⁺] = 0.016 M; pH = 1.8x is not negligible in iii.
• C. i. [H₃O⁺] = 1.2 M; pH = 0.52ii. [H₃O⁺] = 0.12 M; pH = 0.92iii. [H₃O⁺] = 0.016 M; pH = 1.8x is not negligible in all of the given concentrations.
• D. i. [H₃O⁺] = 1.0 M; pH = 0ii. [H₃O⁺] = 0.12 M; pH = 0.92iii. [H₃O⁺] = 0.016 M; pH = 1.8x is not negligible in ii and iii.

Answer: (D)