Two point charges -q and +q are placed at a distance of L, as shown in the figure.

The magnitude of electric field intensity at a distance R(R >> L) varies as:

Concept: 

For finding the magnitude of the magnetic moment of the electric field we should know how it varies with distance. 

We should check whether it is a monopole moment, dipole, or quadrupole moment.

First, we have to check its monopole moment which is known as sum of total charges i.e. m = ∑ Q_i 

where Q = charge placed 

If the monopole moment is zero then the system is independent on considering the frame of the origin or we can consider our origin at any point to make our calculation easier.

Electric dipole moment is = P = ∑ p_i = ∑ q.dx = charge × distance

If it is zero then we have to test its quadrupole moment for the electric field. 

Calculation:

Given:  two charges +q and -q placed at distance L.  

Electric monopole moment is = m = -q +q = 0

Here electric monopole moment becomes zero so we have to calculate its electric dipole moment.

We are free to consider origin anywhere because the monopole moment is zero.

Electric dipole moment is = P = charge × distance (with directions)

The electric field is towards for negative charge and away from the positive charge.

Dipole moment = P = q(L/2) (î) + (-q)(L/2)(-î) = qL (î)

so here, the dipole moment is non-zero. we know that for dipole moment electric field varies as E ∝ 1/R³ 

Hence Option 3) is correct.