Calculate the relative concentrations of NaH2PO4 and H3PO4 required, giving a solution, which buffers at pH 2.6. (The pKa1 for H3PO4 is 2.1).

Answer 1

The Henderson-Hasselbalch equation is
pH = pKa + log [(base)/(acid)]
You have pH, you can calculate pKa, substitute and solve for (base)/(acid)
Post your work if you get stuck.