Answer:
Mendel's law of dominance
Step-by-step explanation:
Mendel's law of dominance states that in a cross of two "pure" (homozygous) individuals with different traits (white and purple flowers), only one of the traits will appear in the next generation, the dominant one
This is because the next generation inherited one allele for white flowers and one allele for purple flowers, so are heterozygous. The purple flower allele is dominant compared to the white flower allele, so all the offspring are purple. See punnet square attached