Question

can a b positive father and a ab negative mother make a o neg child

Answer 1

A person has two copies of the A/B/O gene, and two copies of the Rh pos/neg gene, one from each parent.
The possible combinations of how the genes are expressed are as follows:
AA = A blood type
AO = A blood type
OO = O blood type
BB = B blood type
BO = B blood type
AB = AB blood type

For Rh factor, it goes like this:
+ + = +
+ - = +
- - = -

So if one parent has B pos, his gene combination could be BB or BO and the Rh factor could be + + or + - . The mother can only be AB - - . So the child got the A gene from the mother, and the B gene from the father, and got both Rh - genes from each parent, making it AB neg.

so according to me O negative child is impossible as the mother do not have any components corresponding to the the blood group O.