Electrostatic field at a distance r from midpoint of a dipole is proportional to?

CONCEPT: 

• Dipole: The measure of the polarity of the system is the electric dipole moment.
• The simplest example of an electric dipole is a pair of electric charges of equal magnitude and opposite signs separated by distance.

At any point at r distance from the dipole, Electric field

$E=\frac{Kp}{r^3}\sqrt{3co{s}^2\theta +1}$

where p is the dipole moment, r is the distance from the dipole, θ is angle, and K is the constant.

EXPLANATION:

At any point at r distance from the dipole, Electric field

$E=\frac{Kp}{r^3}\sqrt{3co{s}^2\theta +1}$

E α 1/r³

So the correct answer is option 3.