Answer
$[Cd(bipy)_{2}]Cl_{2}$
Work Step by Step
The formula is written according to the rules of writing the formula for complex compounds.
1. bis(bipyridyl)cadmium(II) is the cation whereas chloride is the anion. Cations are written first, then are anions.
2. bis(bipyridyl) is the ligand whereas cadmium(II) is the metal. Metal is written first then is the ligand.
3. Bis(bipyridyl) means two bipyridyl. Thus, $(bipy)_{2}$
4. From point 2 and 3 we have, $[Cd(bipy)_{2}]$
5. Cadmium (II) means Cadmium has a +2 charge. Chloride has a -1 charge $Cl^{-}$ . In order to check if the charge on Cation and anion is balanced, we take out the charge on cation first:
$+2+ 2\times (0)$
$+2$
6. In order to balance charges, we need two chloride. Thus, $Cl_{2}$
Therefore the formula of the complex is:
$[Cd(bipy)_{2}]Cl_{2}$
