Answer : As per the definition of the buffer solution "It is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa".
so considering the above given condition for [tex]CH_{3} COOH[/tex] and [tex]NaCH_{3}CO_{2}[/tex] act as buffer because it satisfies and qualifies the conditions of behaving as a buffer when mixed in equal amounts,
whereas HCl and NaOH are strong acid and strong base which does not satisfies the criteria for being called as buffer.
As buffer needs a weak acid and its conjugate base to behave and act as buffer and resist any pH change.