Apea plant is heterozygous (aa) for seed color and heterozygous (bb) for seed shape. according to mendel's principle of independent assortment:

According to Mendel’s principles of independent assortment is that a gamete that receives a dominant allele for the colour of the seed, it is equally likely to receive the allele dominant for the shape of the seed as it is in the recessive allele for the shape of the seed.

i thinking chemical change