(a) (i) In the figure, OA and OB show the variation of electric potential V at a point due to two point charges $Q_1$ and $Q_2$ with $\frac{1}{r}$ respectively. Here r represents the distance of the point from the two point charges. (I) Identify the nature of the two charges $Q_1$ and $Q_2$. (II) What is the value of $\left$ \frac{Q_1}{Q_2} \right$$? Justify your answer. (ii) Two point charges $-2 \mu\text{C}$ and $5 \mu\text{C}$ are placed at $(-30 \text{ cm}, 0)$ and $(30 \text{ cm}, 0)$ respectively in an external electric field $\vec{\text{E}} = \frac{\text{A}}{\text{x}^2} \hat{\text{i}}$, where $\text{A} = 9 \times 10^5 \text{ Nm}^2 \text{C}^{-1}$. Find the electrostatic potential energy of this configuration.