4. X-ray radiation from diffraction and fluorescence instruments is a) Not very dangerous because the X-rays are absorbed in the air b) Very dangerous but poses little real hazard since instruments are designed to completely enclose all beams c) Very dangerous and users must not override devices designed to protect from exposures d) Dangerous only when at full power

c) Very dangerous and users must not override devices designed to protect from exposures.

Explanation:

X-ray is a form of high energy electromagnetic radiation and are part of the electromagnetic spectrum.

X-ray radiation from diffraction and fluorescence instruments is very dangerous because of their high energy and wavelength.

Hence, users must not override devices designed to protect from exposures. The best shielding device to protect one from exposure is Lead.