question_answer

The oxidation number, d-orbital occupation and coordination number of Cr in the complex cis\[[Cr{{(en)}_{2}}C{{l}_{2}}]Cl\]are respectively

A)  +3, 3d and 4      

B)  +3, 4d and 6

C)  +3, 3d and 6     

D)  +2, 3d and 6

Correct Answer: C

Solution :

                Let the oxidation number of Cr is\[x\]. \[cis[Cr{{(en)}_{2}}C{{l}_{2}}]Cl\] \[x+(0)\times 2+(-1)\times 2-1=0\] \[x-3=0\] \[x=+3\] In\[[Cr{{(en)}_{2}}C{{l}_{2}}]Cl,\]the Cr atom is present as\[C{{r}^{3+}}\].                 \[C{{r}^{3+}}=[Ar]\,3{{d}^{3}}4{{s}^{0}}\] \[cis[Cr{{(en)}_{2}}C{{l}_{2}}]=[Ar]\] (en being a strong field ligand, can cause pairing.) Thus, 3d orbitals are occupied. Since, two\[Cl\]atoms (monodentate) and two ethylene   diammine,   ie,   en   molecules (didentate) are linked two the central atom, the coordination number of central atom