When mendel crossed purebred purple flowering plants (pp) with purebred white flowering plants (pp), what were the flower colors of the resulting offspring? 25 percent white and 75 percent purple 50 percent white and 50 percent purple 100 percent purple 100 percent white

The answer is 100 percent purple

Let P be dominant allele for purple flowers and p recessive allele for white flowers. So purebred purple flower has two P alleles and its genotype is PP and purebread white flower has two p alleles and its genotype is pp. Since P is dominant over p, when found together like in heterozygous plants (Pp), the flowers will express dominant allele and will be purple.
So, a cross between purebred purple flowering plants (PP) with purebred white flowering plants (pp) will have 100% of the offspring with genotype Pp and purple flower color.

Parents:               PP      x       pp
Offspring:        Pp     Pp      Pp    Pp