Phosphoric Acid, H₃PO₄, Is a Triprotic Acid, for Which K_a1

Multiple Choice

Phosphoric acid, H₃PO₄, is a triprotic acid, for which K_a1 = 7.2 × 10⁻³, K_a2 = 6.3 × 10⁻⁸ and K_a3 = 4.2 × 10⁻¹³. What is the value of K_b for the hydrogen phosphate anion, HPO₄?

A) 6.3 × 10 ⁻⁸
B) 4.2 × 10 ⁻¹³
C) 1.4 × 10 ⁻¹²
D) 1.6 × 10 ⁻⁷
E) 2.4 × 10 ⁻²