KBC 2021: What does the letter 'X' denote in X-Ray?

Options:

1) Xenon

2) Unknown

3) Illegal

4) Radiation

Answer: Unknown 

Even though the meaning of 'X' in X-ray is unknown, the second half of the term stands for radiation. X-ray tech is widely used for medical applications. X-ray was discovered in 1895 by German scientist Wilhelm Conrad Röntgen.

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