Why is there such great diversity among organic compounds?
a. carbon has many allotropes
b. carbon has many isotopes
c. carbon compounds have many isomers
d. carbon compounds are very reactive

The best and most correct answer among the choices provided by the question is the first choice "carbon has many allotropes"

Organic compound, any of a large class of chemical compounds in which one or more atoms of carbon are covalently linked to atoms of other elements, most commonly hydrogen, oxygen, or nitrogen. The few carbon-containing compounds not classified as organic include carbides, carbonates, and cyanides.

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D-no effect on the rate