Final answer:
The correct entry for the upper right box in the Punnett square is 'b'. The offspring in that box would have the genotype 'bb', which means they will have the recessive allele for flower color and have white-colored flowers.
Step-by-step explanation:
The correct entry for the upper right box in the Punnett square is b. The Punnett square shows a cross between two parents, one with alleles BB and the other with alleles Bb. The upper right box represents the possible genotypes of their offspring. In this case, the offspring in that box would have the genotype 'bb', which means they will have the recessive allele for flower color. This means that the offspring will have the recessive trait of white-colored flowers.