these are conjugate bases of the following acids HBr , HNO2 , HCN , HCl....

as we know that HCl and HBr are strong acids so their conjugate base will be very weak ...

so ans is Br- and Cl-

CN- and NO2- are conjugate bases of weak acids HCN and  HNO2 ....so they are strong

Basic anions – act as weak bases in water

– The anions (conjugate bases) of weak acids (F-,CN-, S2-, PO43- …) act as weak bases

Neutral anions – do not influence the pH

– The anions (conjugate bases) of strong acids (Cl-,Br-, I-, NO3-, ClO4-…) are extremely weak bases

(weaker than H2O) so they do not influence the pH

4) HCN and NaF won't. 5) NaBr and KBr won't. 7) NaCl and KCl won't A buffer is a answer of a mix of an acid and its conjugate base. Acetic acid and a sodium acetate. it is an invaluable technique mainain a relentless pH of a answer If acid is extra desirable the acdetate ion reacts with it annd remoces ir , I o=OH - is upload the acetic acid removes it. a million), 2) 3) 6) Will act asbuffers.

Idk why this is the answer but the answer on mastering chemistry is CN- and NO2-