Which one of the following blood groups is impossible in offspring if blood groups of parents are A and AB?

Correct option is A

Blood group inheritance follows the principles of Mendelian genetics. The A and B blood group alleles are dominant, while the O allele is recessive. If one parent has an A blood group (genotype AA or AO), and the other has an AB blood group (genotype AB), the possible blood types of their offspring are A, B, or AB.

However, it is impossible for the offspring to have an O blood group because the O group requires both parents to pass on an O allele. Since the parent with blood group AB has no O allele to pass, the child cannot have blood group O.