When X-rays are produced, heat is generated at the target. This is because X-rays are produced through a process called bremsstrahlung, in which high-speed electrons collide with the target material (usually a metal). These collisions cause the electrons to rapidly decelerate, releasing energy in the form of X-ray photons. However, in the process of deceleration, the electrons also transfer some of their kinetic energy to the atoms in the target material, leading to the generation of heat.

Option 2 stating that heat is absorbed at the target is not accurate. The production of X-rays involves the conversion of kinetic energy from the moving electrons into X-ray photons, which results in the generation of heat energy at the target.

Option 3 stating that the temperature of the target remains constant is not accurate either. The generation of X-rays involves the transfer of energy to the target material in the form of heat, so the temperature of the target will increase as a result.

Option 4 stating that brilliant light is seen at the target is also not accurate. X-rays are not visible light; they have a higher frequency and shorter wavelength than visible light and cannot be seen with the naked eye.

In conclusion, when X-rays are produced, option 1 - heat is generated