Exception to Mendel's law

Answer: Option D

The exception to Mendel's law is Mirabilis.
Mendel described dominance but not incomplete dominance. Had he worked with Mirabilis jalapa rather than pea he would have pondered the cross of a plant with red flowers by one with white flowers.
All progeny were pink flowered, an intermediate phenotype. An individual who is heterozygous for a gene has two different alleles, but it is not always sufficient to produce an intermediate phenotype.