Answer
$NaH_2PO_4$ and $Na_2HP{O_4}$ are the best combination for this solution.
Work Step by Step
1. Identify the acid:
$- H_2PO_4$:
2. Calculate its pKa:
$pKa = -log(Ka)$
$pKa = -log( 6.3 \times 10^{- 8})$
$pKa = 7.20$
3. Compare this number to 7.
$7.20$ is very close to 7, therefore, this is the best combination for a pH neutral buffer.
