Assertion: Intensity of X− can be controlled by adjusting the filament current and voltage.
Reason: The intensity X−rays does not depend on the number of X− rays photons emitted per second from the target.
A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If the assertion is true but the reason is false.
D. If the assertion and reason both are false

Hint: The X-Rays' intensity and hardness varies from one another. Hardness describes the type of radiation that is focused, whereas intensity is the amount of radiation that is concentrated per square inch on the target. By adjusting the voltage of the incident beam and subsequently changing the current's intensity, hardness can be changed.

Complete step by step solution:
A heavy metal target serves as the anode in an X-ray tube, which is a comparatively straightforward electrical device made up of a cathode filament. Electrons from the cathode filament are released when a voltage is supplied across the apparatus, and they go to the heavy metal target anode and strike it. Their energy, which is released as X-ray photons, is lost as a result.

Now, if the filament current is increased, the filament temperature will rise and a bigger number of electrons will be emitted as a result of the higher thermal energy. As a result, more electrons will strike the metal target in a given period of time, causing a higher release of X-ray photons. In essence, this will mean that the X-rays would become more intense.

The square of the voltage and the filament current are both directly related to X-ray intensity. It is generally known that the number of photons a target emits per second determines the intensity of X-rays.

Hence option C is correct.

Note: The cathode filament emits electrons as it warms up. The amount of electron emission increases as the filament heats up. x-rays with a wide range of constant energy. The kinetic energy of the electrons impacting the anode is equal to the maximal energy of the x-rays.