Explanation:
An allotrope is defined as one or more form of a chemical element that exist in same physical state but different chemical properties.
For example, allotropes of carbon are graphite and diamond. And, both of them exist in a solid state with different chemical properties.
On the other hand, an isotope is two or more forms of an element that contains same number of protons but different number of neutrons.
For example, [tex]^{2}_{1}H[/tex] and [tex]^{3}_{1}H[/tex] are isotopes of hydrogen.
Some of the differences between allotropes and isotopes are as follows.
one or more forms of a chemical element that occur in the same physical state. ... Allotropes may display very different chemical and physical properties. For example, graphite and diamond are both allotropes of carbon that occur in the solid state.