Answer:
RbF
mgo
nh4cl
because electrons are lost by and element forming a cation and gained by the other element forming an anion and held together by electrostatic forces
I do not see any mistakes so I think you’re good!

Actually Welcome to the concept of Bond Formation.
Answer is :-
B.) O and Cl
These both are Non-Metals with high Electronegativity nature, hence none of them can share electrons to foram any bond to eventually form a Electro valentines Compound.