Radiation

Assertion (A) is false: X-rays are produced when high-speed (not slow) electrons strike a metal target (like tungsten) with a high atomic number. The sudden deceleration of these electrons leads to emission of X-rays, a phenomenon known as Bremsstrahlung or braking radiation. Therefore, the statement about "slow moving electrons" is incorrect. Reason (R) is also false: X-rays are high-energy photons, with energies typically in the range of 1 keV to 100 keV or more. They lie well above the visible spectrum in terms of energy. Hence, calling them "low-energy photons" is factually wrong. Since both statements are incorrect, the correct answer is option (D).