In radishes, red and white are pure-breeding colors, while hybrids are purple. if a red radish is crossed with a white radish, what will be the phenotype of the f1 generation.?

The first part of the question - about pure breeding - says that red radishes and white radishes are both homozygotes for color. It doesn't say anything about how many genes or alleles of a single gene are involved. It also doesn't say anything about which of white and red are dominant and recessive. The second part of the question - about hybrids being purple - tells you that which ever allele is dominant, it is incompletely dominant. That is, heterozygotes with one dominant allele and one recessive allele have an intermediate phenotype between the two homozygous phenotypes. You know that the red radishes are one sort of homozygote; white radishes are the other sort of homozygote. Set up a Punnett Square AA x aa and see what you get for offspring, bearing in mind that heterozygous offspring Aa are all purple. (the answer would be a purple Aa radish).