Given, charge of dipole, $q=500 \times 10^{-6} \mathrm{C}$
Separation between charges, $2 a=10 \mathrm{~cm}$
$$
=10 \times 10^{-2} \mathrm{~m}
$$

Distance of location from mid point of axis,
$$
r=25 \mathrm{~cm}=25 \times 10^{-2} \mathrm{~m}
$$

$\because$ Electric field on axis of dipole,
$$
E=\frac{4 k q a r}{\left(r^2-a^2\right)^2}
$$
where, $k$ is Coulomb's constant $=9 \times 10^9 \mathrm{C}^2 \mathrm{~m}^{-2} \mathrm{~N}^{-1}$
$$
\begin{aligned}
& 4 \times 9 \times 10^9 \times 500 \times 10^{-6} \\
& \Rightarrow \quad E=\frac{\times 5 \times 10^{-2} \times 25 \times 10^{-2}}{\left[\left(25 \times 10^{-2}\right)^2-\left(5 \times 10^{-2}\right)^2\right]^2} \\
& =\frac{2.25 \times 10^5}{[0.0625-0.0025]^2} \\
& =\frac{2.25 \times 10^5}{(0.06)^2} \\
& =\frac{2.25 \times 10^5}{3.6 \times 10^{-3}} \\
& =6.25 \times 10^7 \\
& \approx 6 \times 10^7 \mathrm{NC}^{-1} \\
&
\end{aligned}
$$

The result is close to option (a).