A man with blood group B and a woman with blood group O, will have children with blood group ------.
a. B or O
b. AB, A, B or O
c. AB or O
d. A or O

Hint: A blood type is a grouping of blood, based on the presence and absence of antibodies and hereditary antigenic substances on the surface of red blood cells. These antigens may be carbohydrates, proteins, glycolipids or glycoproteins, depending on the blood group system.

Complete answer:
There are 4 main types of blood (blood groups) – A, B, AB and O. Each group can be either RhD positive or RhD negative, that will make a total of 8 blood groups.
A RhD positive (${A^ + }$)
A RhD negative (${A^ - }$)
B RhD positive (${B^ + }$)
B RhD negative (${B^ - }$)
O RhD positive (${O^ + }$)
O RhD negative (${O^ - }$)
AB RhD positive ($A{B^ + }$)
AB RhD negative ($A{B^ - }$)
Also, human blood type is determined by codominant alleles. There are three different types of alleles for human blood type and those are i.e \[{I^A},{\text{ }}{I^B}\] and i. For understanding, we can call these alleles A (for \[\;{I^A}\]), B (for \[{I^B}\]), and O (for i).

If the blood group of the father is B and his genotype is ${I^B}$${I^O}$, and the blood group is the mother is O, and her genotype is ${I^O}$${I^O}$then the blood group of the children can be B or O only.

Hence, the correct answer is option (A).

Note: Receiving blood from the wrong ABO group can be life-threatening. Let’s say, if someone with blood group B is giving blood to a person with blood group A, their anti-A antibodies will attack the group A cells. But as we know group O red blood cells do not have any A or B antigens, it can safely be given to any other group.