To Simulate the PH of Blood, Which Is 7

To simulate the pH of blood, which is 7.4, a buffer solution made by dissolving sodium dihydrogen phosphate (K_a = 6.2 *10^-8) and sodium hydrogen phosphate (K_a= 3.6 *10^-13) together in an aqueous solution can be used.What mole ratio of Na₂HPO₄/NaH₂PO₄ is required to produce a solution with a pH of 7.4?

A) 1.2
B) 1.6
C) 0.90
D) 1.0
E) 0.96