What are substances that have the same composition, but different structures, known as?

a.

Ions

c.

Allotropes

b.

Covalent twins

d.

Phenotypes

Verified Answer :

The answer is Allotropes.

For the answer to the question, what are substances that have the same composition, but different structures, known as? I believe the answer to this problem is the second one among the given choices which is Allotropes.
I hope my answer helped you.