The correct answer is option 'C': The X-ray beam coming from an X-ray tube has all wavelengths greater than a certain minimum wavelength.

Explanation:
X-rays are a form of electromagnetic radiation that have shorter wavelengths and higher energy than visible light. X-ray tubes are devices that generate X-rays by accelerating electrons to high speeds and directing them at a target material. When these high-speed electrons collide with the target material, they release energy in the form of X-rays.

In an X-ray tube, the electrons are accelerated through a high voltage potential difference, causing them to gain kinetic energy. When these high-energy electrons strike the target material, they undergo a process called Bremsstrahlung radiation. This process involves the deceleration of the electrons, resulting in the emission of electromagnetic radiation, including X-rays.

The X-rays produced in an X-ray tube have a wide range of wavelengths. This is because the energy of the X-rays emitted depends on the energy of the electrons and the specific interactions that occur between the electrons and the target material. As a result, X-rays with different wavelengths (and hence different energies) are emitted.

The minimum wavelength of the X-rays produced in an X-ray tube is determined by the energy of the electrons. As the energy of the electrons increases, the minimum wavelength of the X-rays decreases. Therefore, the X-ray beam coming from an X-ray tube has all wavelengths greater than a certain minimum wavelength.

It is important to note that X-rays generated in an X-ray tube are not monochromatic (option 'A'), meaning they do not have a single wavelength. They also do not have all wavelengths smaller than a certain maximum wavelength (option 'B') as X-rays can have very short wavelengths. Option 'D' is incorrect as the X-ray beam does not have a specific range of wavelengths lying between a minimum and a maximum wavelength.

In conclusion, the correct answer is option 'C': The X-ray beam coming from an X-ray tube has all wavelengths greater than a certain minimum wavelength.

The X ray beam coming from an x-ray tube has all wavelength greater than a certain minimum wavelength and that minimum wavelength is called thresold wavelength.