Based on this information, what is this plant's phenotype for the flower color trait?

 - red flowers
 - white flowers
The scarlet rosemallow plant's genotype for the flower color gene is FF. The scarlet rosemallow plant's genotype of FF has only F allelles. The F allele is for red flowers. So, the scarlet rosemallow plant's phenotype for the flower color trait must be red flowers.
To check this answer, consider whether the scarlet rosemallow plant's alleles are dominant or recessive. The allele for white flowers (f) is recessive to the allele for red flowers (F). This means F is a dominant allele, and f is a recessive allele.
The scarlet rosemallow plant's genotype of FF has two dominant alleles. An organism with at least one dominant allele for a gene will have the dominant allele's version of the trait. So, the scarlet rosemallow plant's phenotype for the flower color trait must be red flowers.