1. Find its coordination figure/coordination number of central atom (CF)
Ev = Vallence electron of central atom
Σe = electrons donated from substituents
Terminal O gives 0 electrons, hence Σe = 3 x 0
charge = charge of the compound
2. Find EP (electron pairs) and LP (lone pairs)
LP = CF - EP
3. Draw the skeleton with octet substituents (top right figure)
4. Find formal charge for each atoms (Qf)
5. Write formal charge near atom in skeleton
6. Enjoy
Explanation:
here's the answer to your question
C. Because you eliminate "spectator ions" or ions that are repeated and you can only do that to aqueous. So, Ca +2 and 2I -1 are the only ones you can remove for net ionic.