As a technician in a large pharmaceutical research firm, you need to produce 350 mL of a potassium dihydrogen phosphate buffer solution of pH = 7.06. The pKa of H₂PO₄− is 7.21. What is the required concentration of KH₂PO₄ for this buffer?
A) 0.10 M
B) 0.50 M
C) 1.0 M
D) 2.0 M