Does H4N2O2 exist as a compound?
yes
If you wrote it as NH4NO2 would it make more sense to you. And to answer the next question, then compound C is NH4NO3. (H4N2O3).
Discuss briefly the relationshiop between the dipole moment of a molecule and the polar character of the bonds within it. With this as a basis, account fot he difference between the dipole moments of CH2F2 and CF4.