What Is The Blood Group Of A Child Whose Mother Is O+ And Father Is B+?

Impossible to be sure.
There are two genes that encode for blood type in the human genome. On the mother's side, both would be O. The father, however, could be homozygous (BB) or heterozygous (BO) and still have type B blood.
If the father is BB, then all of the children will inherit a B gene from him and an O gene from their mother, and they will be type B. If the father is BO, then there is a 50% chance the child will inherit the B gene and be type B, and a 50% chance the child will inherit the O gene and be type O.

Most likely, the child will be Rh positive. I'm really not sure on the probability there.

O positive mother can pass on only o .  Regarding the rhesus factor she can pass on rh pos but if she is NOT pure breeding for this and is +- in her genotype then she could also pass on the rh neg. /////The father being B+?? He may be BB or Bo and therefore can pass on B  definately but maybe also the o if not pure breeding for his B type. Re his rh factor, he can be ++  or +- and therefore he can pass on  +definately but maybe also - too. So it depends on their genotypes as to what chances of child are  I can tell u definately what children cannot arise from such a union and that is type AB and also type A

The child should be  B positive