Which of the following is not a mendelian disorder?

The correct option is D Colour blindness
Colorblindness is an X- linked recessive disorder. One copy of the affected gene in males results in color blindness as males have a single copy of X chromosome(X${}^c$Y). Females with two copies of the affected gene have the disease (X${}^c$X${}^c$). A female with a single copy of the affected gene will be a carrier. Hence it is not a Mendelian disorder. Thus the correct answer is option A.