There are two kinds of buffer solutions:

Acidic buffers: A weak acid and the salt of its conjugate base.
Ex. WO NA
Basic buffer: A weak base and the salt of its conjugate acid.
ex. .
Here, option is not correct because, HCl is a strong acid. option is also incorrect because, is a salt of weak acid and is also a weak acid.
option is again incorrect. because, NaCl is a salt of strong acid and NaOH is a strong base.
Hence, option is correct as NaCN is a salt of weak acid & strong base and HCN is a weak acid. Therefore, these can act as a buffer.