The alphabet X in X-ray stands for _______ ray.
- AExpress
- BUnknown
- CInfrared
- DXenon
- ENone of the above/More than one of the above
Show answer and explanation
Correct answer: (b) Unknown
Explanation
Wilhelm Röntgen, who discovered X-rays in 1895, called them "X" because their nature was then unknown, as x stands for an unknown in mathematics.
X-rays are high-energy electromagnetic waves, used in medical imaging, airport security and crystallography.