Final answer:
The question about finding BC cannot be answered due to insufficient context and information provided.
Step-by-step explanation:
The question seems to contain a typo or an error as it does not provide sufficient context or information about what BC represents and which mathematical concepts are being applied. The data provided relates to the Periodic Table of Elements and some numerical data sets that do not correlate with finding the length of segment BC. Without additional information such as a figure or a description of the geometrical setup, it is not possible to provide an accurate answer to find BC.