Ionic bonding is a strong type of bonding, in which will occur predominantly with metals + nonmetals, because of their difference in electronegativity, so for our question, we are looking for metals and nonmetals together since they are likely to form ionic bonds
A. RbCl and MgO
In this case, we have a situation that perfectly follows the explanation, a metal + nonmetal, both compounds are ionic
B. Na2SO3 and NH3
Although we have an ionic bonding with Na2SO3, NH3 will present a more covalent type of bonding
C. SC12 and HF
HF is considered to be covalent
D. BaF and H2O
H2O is a polar covalent compound, it has charges but not as much as an ionic compound
Therefore the best answer will be number 1 or letter A