In 1960, which isotope was used to define the standard measure of length?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. Krypton-86.
In 1960, the isotope Krypton-86 (specifically Krypton-86 gas) was used to define the standard measure of length, which is the meter. The international definition of the meter was based on the wavelength of light emitted by Krypton-86 atoms. This definition was used until it was replaced in 1983 by the current definition based on the speed of light.