How is a gene different from an allele?

A gene is a fragment of DNA, the allele is a possible variation of a gene.

Explanation:

Genes contain hereditary information, that codes this information for the transmission of inherited traits.

Each gene resides at a specific location on a chromosome, in two copies, one inherited from each parent.

These copies are not necessarily the same.

When the copies of a gene differe from each other, they are called alleles.

Even genes may have multiple alleles, only two alleles are present  at the gene's locus on any individual.

I hope it helps!

i am positive it is c. condensing but i may be wrong