Answer
Drawing number $(i)$ is the appropriate representation for that situation.
Work Step by Step
When $NaOH$ is added to a weak acid solution, this reaction will happen:
$HA(aq) + NaOH(aq) -- \gt A^-(aq) + Na^+(aq) + H_2O(l)$
Therefore, the concentration of $[HA]$ is decreasing, and the $[A^-]$ is increasing.
The figure that represents that situation is the number $(i)$
