Identify a mixture from the following solution pairs where equal volumes of the two solutions, when mixed together, will lead to the formation of a buffer.

a) 0.13 M HCl with 0.15 M NaOH

b) 0.13 M H₂SO₄ with 0.13 M Na₂CO₃

c) 0.26 M HCN with 0.13 M KOH

d) 0.10 M NH₄Cl with 0.20 M HCl