Work Step by Step
Atomic weight: $135.9090×0.193/100+137.9057×0.250/100+ 139.9053×88.48/100+141.9090×11.07/100= 140.1046$ The closest atomic weight is cerium's.
You can help us out by revising, improving and updating this answer.Update this answer
After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.