Answer
(b) $HF/KF$ and (c) $NH_3/NH_4Cl$
Work Step by Step
- A buffer must have a weak conjugate acid-base pair.
(a) $HCl$ is a strong acid, so it cannot form a buffer with $Cl^-$
(b) $HF$ is a weak acid, and $KF$ has $F^-$, so they can form a buffer.
(c) $NH_3$ is a weak base, and $NH_4Cl$ has $N{H_4}^+$, so they can form a buffer.
(d) $HNO_3$ and $HNO_2$ aren't a conjugate pair.
(e) $N{O_2}^-$ and $HNO_3$ aren't a conjugate pair.
