Answer
See the detailed answer below.
Work Step by Step
$$\color{blue}{\bf [a]}$$
A dipole of charges $\pm 2\;\rm nC$ exerted an electric field of 1150 N/C at a distance of 2.5 cm on a plane that bisects the dipole. Find its length.
$$\color{blue}{\bf [b]}$$
Solving the given formula for $s$,
$$s=\dfrac{(1150)(0.025)^3}{(2\times 10^{-9})(9\times 10^9)}\approx \color{red}{\bf 1}\;\rm mm$$
