Question

All noble gases crystalline in the ccp structure except:

• A. helium
• B. neon
• C. argon
• D. krypton

Answer 1

The correct option is A helium

All noble gases crystallize in the ccp structure except helium which has two allotropes, one in hcp structure and the other in bcc structure.

Contrary to theoretical calculations that helium should be in the face- or body-centered cubic structure, in the entire range of pressures of this study, the measurements demonstrate that helium crystallizes in hexagonal-close-packed structure (Fig.), which is the same as that of solid hydrogen under these conditions