Iron Exhibits Polymorphism, the Ability of a Solid Material to Exist

question 135

Multiple Choice

Iron exhibits polymorphism, the ability of a solid material to exist in more than one crystal form.At low to moderate temperatures, it adopts a bcc structure; at temperatures above 913 $\degree$ C, it adopts an fcc structure.Silicon carbide also has polymorphs, including the wurtzite form with abab packing and the sphalerite form with abcabc packing.Which of the following statements is NOT correct?

• A)The bcc and fcc forms of iron probably have the same densities.
• B)The packing efficiency of iron atoms in the bcc form is lower than that of the fcc form.
• C)The two silicon carbide polymorphs probably have the same densities.
• D)The packing efficiencies of the two silicon polymorphs are probably the same.
• E)Both SiC polymorphs are based on hexagonal packing of atoms.

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