Two point charges +5 $\mu C$ and -5 $\mu C$ are placed at O (0 mm, 0mm) and P(3 mm, 4 mm) respectively force on $+5 \mu C$ is

$1.8(3\hat{i}-4\hat{j})\times 10^{3} N$

The correct answer is option (3) : $1.8(3\hat{i}-4\hat{j})\times 10^{3} N$

Force between two point charge $q_1$ and $q_2$

$\vec{F}=\frac{kq_1q_2(\vec{r}_2-\vec{r}_1)}{|r_2-r_1|^3}$

$\vec{F}=\frac{9\times 10^9 \times 5 \times 5\times 10^{-12} (4\hat{j}+3\hat{i})\times 10^{-3}}{(\sqrt{4^2+3^2})\times 10^{-9}}$

$\vec{F}=1.8(3\hat{i}-4\hat{j})\times 10^{3} N$