Mendel’s pea plants had either purple or white flowers. this means that the plants

The plants were expressing recessive or dominant traits through their flower colours

The answer is that the plants have two alleles of the gene responsible for the color of flowers.

Explanation:

A gene is a part or section of a chromosome that has the genetic information or the code for a particular protein like flower color. Genes may have two or more forms of the particular gene, these forms are called alleles.

There are two alternative forms of the gene for flower color in the case of Mendel's pea plant. The presence of two alternative or distinct forms displays that there must be two alleles of the gene.

Thus, the correct answer that the plants have two alleles of the gene responsible for the color of flowers.