Sentence:  **f appeared to be well suited for the study of these matters , since it is a normal paramagnet , with three unpaired electrons on the chromium , its crystal structure <WSD>is</WSD> very simple , and the unknown position of the hydrogen in the strong **f bond provides structural interest . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)