Basic buffer is the mixture of weak base and its salt with strong acid. In option $\mathrm{A}, \mathrm{NH}_4 \mathrm{OH}$ is weak base and $\mathrm{NH}_4 \mathrm{Cl}$ is salt of strong acid and weak base. Hence, $\mathrm{NH}_4 \mathrm{OH}+\mathrm{NH}_4 \mathrm{Cl}$ is basic buffer. Other options are examples of acidic buffer.