**Visible Spectrum and Wavelength Range**

The visible spectrum refers to the range of electromagnetic waves that can be detected by the human eye. These waves are responsible for the perception of different colors. The visible spectrum is a small portion of the entire electromagnetic spectrum, which includes all types of electromagnetic waves, such as radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. The visible spectrum ranges from approximately 400 to 700 nanometers (nm) in wavelength.

**Explanation of the Options**

a) 4000-8000A: This option suggests a wavelength range of 4000 to 8000 ångströms (Å). However, this range is far outside the visible spectrum and includes longer wavelength waves that are categorized as infrared.

b) 2000-4000A: This option suggests a wavelength range of 2000 to 4000 ångströms (Å). Again, this range is outside the visible spectrum and includes shorter wavelength waves that are categorized as ultraviolet.

c) 10000-20000A: This option suggests a wavelength range of 10000 to 20000 ångströms (Å). Similarly, this range is outside the visible spectrum and includes longer wavelength waves that are categorized as infrared.

d) None of the above: This option implies that none of the provided wavelength ranges fall within the visible spectrum. However, this is not the correct answer.

**Correct Answer**

The correct answer is option 'A' (4000-8000A). This range falls within the visible spectrum and includes wavelengths that correspond to different colors. The lower end of the range (4000 Å) corresponds to violet light, while the upper end (8000 Å) corresponds to red light. The visible spectrum in between consists of colors such as blue, green, yellow, and orange.

**Conclusion**

In conclusion, the broad wavelength range of the visible spectrum is approximately 4000 to 8000 ångströms (Å). This range encompasses the wavelengths of light that can be perceived by the human eye and corresponds to the various colors of the rainbow.

Nahe malum...