Answer: The correct answer is-
C) 75% purple-flowered and 25% white-flowered.
As per the information given in the question, genotypes of parent plants are-
Pp and Pp that is heterozygous dominant, which exhibit purple flowers.
This indicates that purple flower is a dominant trait that masks the expression of recessive trait.
A dominant trait ( depicted by capital letter allele) always masks the expression of recessive trait ( depicted by small letter allele).
When parent plants with heterozygous dominant ( having two different alleles that is dominant and recessive allele) genotype are crossed, they will produce 75% purple-flowered and 25% white-flowered plants.
Refer punnet square.