Which one of the following allotropes of carbon is isomorphous with cr

Which one of the following allotropes of carbon is isomorphous with crystalline silicon?

Coke
Diamond
Graphite
Coal
This question was previously asked in
UPSC NDA-1 – 2022
The correct answer is Diamond. Diamond is a crystalline allotrope of carbon that is isomorphous with crystalline silicon because they share the same crystal structure.
– Isomorphism refers to the phenomenon where two or more substances crystallize in the same crystal structure.
– Crystalline silicon has a diamond cubic crystal structure, where each silicon atom is covalently bonded to four other silicon atoms in a tetrahedral arrangement.
– Diamond, which is also a crystalline allotrope of carbon, also has a diamond cubic structure, with carbon atoms replacing silicon atoms in the same arrangement.
– Coke, Graphite, and Coal are other forms of carbon, but they do not share the same crystal structure as crystalline silicon. Graphite has a layered hexagonal structure, while Coke and Coal are largely amorphous or contain various carbonaceous materials without a single, defined crystal structure.
The similarity in structure between diamond and silicon is due to both carbon and silicon belonging to Group 14 of the periodic table and forming strong covalent bonds in a tetrahedral geometry. This structural similarity has implications for their properties, although the bond strength (C-C vs Si-Si) leads to significant differences in hardness and melting point.
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