The word 'gene' was coined by

Gene is the basic unit of heredity.

A danish botanist Wilhelm Johannsen coined the term gene.

According to Mendel, genes occur in pairs and priorly named them factors.

Later Johannsen also coined the terms genotype and phenotype.

So, option D is the correct answer, term gene was coined by Johannsen, they were named as factors priorly (by Mendel).