Hello!
The most stable isotope of Chromium is ⁵²Cr with a mass of 51,9405 amu.
We know that because of the information that we can find in the periodic table. Which information is that? The atomic weight of the element. Atomic weights are calculated taking into account the relative abundances of each isotope of the element. The isotope that is the most abundant one will influence more the atomic weight that is found in the periodic table.
For chromium, its atomic weight, that we can find on the periodic table, is 51,99 amu. The isotope weight that is nearest to this atomic weight is ⁵²Cr with a mass of 51,9405 amu, so that will be the most stable isotope.
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