## Chemistry: The Central Science (13th Edition)

Drawing number $(1)$ is the best representation for that situation.
Let's use $NaOH$ as an example, when this base is added to the buffer, its acid $(HA)$ will try to neutralize the added base. And this is the reaction: $NaOH(aq) + HA(aq) -- \gt Na^+(aq) + A^-(aq) + H_2O(l)$ Therefore, the concentration of $HA$ is decreasing, and $A^-$ is being produced. The drawing with more $A^-$ and less $HA$ is the first one.