You are tasked with creating 0.500 L of a buffer using the least amount of reagents. It must have a pH of 4.30. Which of the following combinations of acid and conjugate base would be suitable for this buffer?
a. HA with pKa = 4.5 and A⁻
b. HB with pKa = 5.0 and B⁻
c. HC with pKa = 4.0 and C⁻
d. HD with pKa = 5.5 and D⁻