Concept:
For an electric dipole, potential at a point is:
\[
V = \frac{1}{4\pi\varepsilon_0}\frac{p \cos\theta}{r^2}
\]
On axial line, \( \cos\theta = 1 \), so:
\[
V \propto \frac{1}{r^2}
\]
Step 1: Axial point condition
For point on axis:
\[
V = \frac{1}{4\pi\varepsilon_0}\frac{p}{r^2}
\]
Step 2: Proportionality
Since \(p\) and constants are fixed:
\[
V \propto \frac{1}{r^2}
\]
Thus:
\[
\boxed{\frac{1}{r^2}}
\]