Answer
b) $[Cr(H2O)_{4}Cl_{2}]Cl_{2}$ is the right answer.
Work Step by Step
simply just check the set of rules on the following compounds given in the options or we can write compound by using the name given by the iupac rules.
So, tetraaquadichlorochromium(III) chloride is $[Cr(H2O)_{4}Cl_{2}]Cl_{2}$
Therefore (b) $[Cr(H2O)_{4}Cl_{2}]Cl_{2}$ is the correct answer.
