Hello!
A buffer is composed of a weak acid and its conjugate base or a weak base and its conjugate acid. From the given list:
HCl and HF: Strong Acid and Weak Acid. NOT BUFFER
HF and NaF: Weak Acid and Conjugate Base. BUFFER
HC₂H₃O₂ and KC₂H₃O₂: Weak Acid and Conjugate Base. BUFFER
NaOH and NH₃: Strong Base and Weak Base. NOT BUFFER.
Have a nice day!