Question

Which is a pair of allotropes?

A. carbon-14 and carbon-12
B. diamond and carbon dioxide
C. iron(III) oxide and iron(II) oxide
D. molecular oxygen and ozone

Answer 1

A. Carbon-14 & Carbon-12

Answer 2

The answer is D. moleculer oxygen and ozone.
Allotropes are different physical forms of an element. For example, diamond and graphite are allotropes of carbon. (C12 and C14 are isotopes of carbon as they have different numbers of neutrons.)