The correct answer is option 'C', which states that the high voltage used to accelerate electron beams in a color television set is about 25 thousand volts. Let's understand why this is the case.

Television Picture Tube:

A television picture tube, also known as a cathode-ray tube (CRT), is the technology used in older television sets to display images. It consists of a glass envelope containing an electron gun, deflection system, and a phosphor-coated screen.

Accelerating Electron Beams:

The electron gun in a picture tube emits a stream of electrons. These electrons are accelerated towards the screen by a high voltage applied to the anode. The accelerating voltage determines the speed at which the electrons strike the screen and produce the desired brightness and color.

High Voltage Requirement:

To create a bright and clear image on the screen, a high accelerating voltage is needed. This high voltage ensures that the electrons possess sufficient energy to excite the phosphor molecules on the screen, which in turn emit light.

Color Television:

In a color television set, there are three electron guns, each producing a beam of electrons. These beams strike different phosphor dots on the screen, which emit red, green, and blue light. The combination of these three primary colors creates the full-color image.

Voltage Requirement in Color Television:

The high voltage required in a color television set is significantly higher than in a black and white television. This is because the color television requires higher electron beam currents to produce a brighter image and more intense colors. The higher the beam currents, the higher the accelerating voltage required.

Conclusion:

In conclusion, a high voltage of about 25 thousand volts is used to accelerate the electron beams in a color television set. This high voltage is necessary to ensure the electrons possess enough energy to excite the phosphor molecules on the screen and create a bright and vibrant image.