Regarding ABO blood group, if one parent is homozygous and other is heterozygous, what are the chances that their child will have ‘O’ blood group?

The correct option is C $50\%$
Blood group ‘O’ contains both antibodies but no antigens. The alleles $I^A$ and $I^B$ are codominant and are dominant over the allele $I^O(I^A=I^B>I^O)$. If one parent is homozygous $\left(I^O{I}^O\right)$ and other is heterozygous $\left(\frac{I^A{I}^O}{I^A{I}^O}\right)$, their progeny could be

Genotype ratio = 1:1

Therefore, there is $50\%$ chances that the child will have ‘O’ blood group and $50\%$ chances to have blood group either ‘A’ or ‘B’.