Chemistry question about buffers

Question

Which sets of substances can act as buffers? Select all that are correct.

1. NH₃ and NH₄Cl
2. HNO₂ and NaNO₂
3. NaOH and NaCl
4. NH₃ and HCl
5. HCl and NaCl

I would like understand why some substances can be a buffer and what are the correct answers.

Answer 1

NH₃ and NH₄Cl - weak base and conjugate acid

HNO₂ and NaNO₂ - weak acid and conjugate base

NH₃ and HCl - weak base and formation of conjugate acid b/c NH₃ + HCl => NH₄Cl

What you need to make a buffer is a WEAK acid or base, and the conjugate base or acid, respectively.