Two point charges $Q_1$ and $Q_2$ lie along a line at a distance from each other. Figure show the potential verification along the line of charges

Near positive charge net potential is positive and near negative charge potential is negative. So $Q_1$ is positive $Q_2$ is negative, at $1$ potential is zero and this point is near to $Q_2$ . So, magnitude of $Q_1$ is more than magnitude of $Q_2$. Also, slope of$V-r$ graph gives$E,$ which is zero at $3$ .