The pK for the given equilibrium is 7.20.
H₂PO₄⁻ = HPO₄²⁻ + H⁺
The pH of a buffer prepared using H₂PO₄⁻ and HPO₄²⁻ is 7.40. The ratio [HPO₄²⁻] /[H₂PO₄⁻] is
• 0.50
• 1.00
• 1.58
• 0.63