Answer
The atomic mass of 51.9961 Da means that chromium exist predominantly as atoms. A more likely possibility is that chromium exists as a mixture of isotopes with weighted average atomic mass is 51.9961 Da. For zinc, we should deduce two or more isotopes. The weighted average atomic mass, which is 65.409 Da, is too far from 65 Da to suggest a single isotope (a single mass).
Work Step by Step
The atomic mass of 51.9961 Da means that chromium exist predominantly as atoms. A more likely possibility is that chromium exists as a mixture of isotopes with weighted average atomic mass is 51.9961 Da. For zinc, we should deduce two or more isotopes. The weighted average atomic mass, which is 65.409 Da, is too far from 65 Da to suggest a single isotope (a single mass).
