Given

Calculation for Assertion (A):The potential at an axial point of a dipole is given by:
$$V=\frac{1}{4\pi {ϵ}_0}\cdot \frac{P\cos \theta }{r^2}$$
For axial points, $\theta =0^{\circ }$ or $180^{\circ }$, so $\cos \theta =\pm 1$.
$$V=\pm \frac{9\times 10^9\times 4\times 10^{-6}}{2^2}=\pm \frac{36\times 10^3}{4}=\pm 9\times 10^3\text{V}$$
So, Assertion (A) is true.Analysis of Reason (R):The formula for electric potential at an axial point is $V=\pm \frac{P}{4\pi {ϵ}_0{r}^2}$.The Reason states $V=\pm \frac{2P}{4\pi {ϵ}_0{r}^2}$, which is incorrect (this looks like a confused version of the electric field formula $E=\frac{1}{4\pi {ϵ}_0}\frac{2P}{r^3}$).Since the formula in the Reason is wrong, Reason (R) is false.