Which statement about allotropes is true?

• A. Allotropes are different chemical compounds with different elements
• B. Allotropes are different crystal structures of the same element
• C. Allotropes involve changes in chemical composition
• D. Allotropy occurs only at extreme temperatures

Answer: (B)

Allotropes are different crystal structures of the same element. This means the atoms are arranged in distinct ways, giving different properties even though the chemical formula stays the same. For example, carbon exists as diamond, with a strong three-dimensional network, and graphite, with layered sheets that can slide past one another—both are forms of carbon, just arranged differently. Oxygen also has allotropes, such as O2 and O3 (ozone), which are the same element in different structural forms. These variations come from changes in bonding and arrangement, not from adding or removing elements or changing composition. Allotropy isn’t limited to extreme temperatures; it can occur under a range of conditions.