Which of the following pairs of substances, when mixed in any proportion you wish, can be used to prepare a buffer solution? (Select all that apply.)

Question

NaCN and HCN
NaCN and NaOH
HCN and NaOH
HCl and NaCN
HCl and NaOH

and Which of the following gives a buffer solution when equal volumes of the two solutions are mixed? (Select all that apply.)

0.10 M NH3 and 0.10 M HCl
0.20 M NH4Cl and 0.10 M NaOH
0.20 M NH3 and 0.10 M HCl
0.10 M NH4Cl and 0.10 M NH3

I know the second one is at least .20M NH3 and .10M HCl but idk what else

Answer 1

NaCN and NaOH
HCN and NaOH
HCl and NaCN
HCl and NaOH