Final answer:
Characteristic radiation occurs when an electron fills an inner-shell vacancy in an atom, with the emitted x-ray energy being distinct to that element, such as approximately 69 keV for tungsten.
Step-by-step explanation:
The radiation produced at very discrete energies of approximately 69 keV when electrons interact with the K shell of the tungsten target atom is called Characteristic radiation. This form of x-ray radiation occurs when an electron makes a transition to fill an inner-shell vacancy, particularly in heavy elements like tungsten.
High accelerating voltages are required to eject inner-shell electrons, and in the case of tungsten, this is at least 72.5 kV. When such an inner-shell vacancy is filled, especially for the n = 1 shell in tungsten, the photon energy is distinctly characteristic of the element.
Radiation produced at very discrete energies of approximately 69 kiloelectron volts (keV) when electrons interact with the K shell of the tungsten target atom is called characteristic radiation.
Therefore the correct option is 2) Characteristic radiation.