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 <WSD>chromium</WSD> , its crystal structure is 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:  a hard brittle multivalent metallic element; resistant to corrosion and tarnishing