Which of the following was invented by Wilhelm Roentgen?

The correct answer is B) X-Ray Machine. Wilhelm Conrad Roentgen, a German physicist, observed in November 1895 that a fluorescent screen glowed when a Crookes tube was operated nearby, even through black cardboard. He called the unknown radiation X-rays. Strictly speaking, he discovered X-rays rather than invented them, and the machine built around the X-ray tube came later through others. The question intends Roentgen's X-rays, and he received the first Nobel Prize in Physics in 1901.

• A) Radio: Heinrich Hertz demonstrated radio waves in 1887, and Guglielmo Marconi developed practical wireless telegraphy. Roentgen had no role in it.
• C) Electric Bulb: The practical incandescent bulb is credited to Thomas Alva Edison and Joseph Swan around 1879-80, not Roentgen.
• D) None of the above: Incorrect, because option B is the intended answer.

The core concept is the electromagnetic spectrum. X-rays are short-wavelength, high-energy radiation used in medical imaging and in crystallography. For Mains, this links to science and technology in daily life and to the ethics and safety of radiation use.

Trap: Aspirants pick Radio or Electric Bulb because those are famous inventions of the same era, and they ignore the specific link between Roentgen and X-rays.