1. Useful power emitted as light

The source has total power $100\,\text{W}$ and emits light with $5\%$ efficiency.

So, radiant power in the form of light is

$P_{\text{light}} = 0.05 \times 100 = 5\,\text{W}$

2. Intensity at distance $r=5\,\text{m}$

For a point source radiating uniformly in all directions,

$I_{\text{total}} = \frac{P_{\text{light}}}{4\pi r^2}$

Substituting values:

$I_{\text{total}} = \frac{5}{4\pi (5)^2} = \frac{5}{100\pi} = \frac{1}{20\pi}\,\text{W/m}^2$

3. Intensity due to electric field component

In an electromagnetic wave, the energy is equally shared by electric and magnetic fields.

Hence, intensity associated with the electric field component is

$I_E = \frac{1}{2} I_{\text{total}} = \frac{1}{2}\times \frac{1}{20\pi} = \frac{1}{40\pi}\,\text{W/m}^2$

4. Match with options

$\boxed{\frac{1}{40\pi}\,\text{W/m}^2}$

So the correct option is A.