## Chemistry: The Central Science (13th Edition)

The ligands $(NH_{3})_{2}$ and $(NCS)_{4}$ that surround the central metal atom $Cr$ are 2+4=6, therefore the coordination number is 6. Let us suppose the oxidation number of $Cr$ is $x$. To find the oxidation number, we sum the known oxidation numbers and equal it to the charge on the complex. Also, $NH_{4}= +1$ $(NH_{3})_{2}=2 \times 0$ $(NCS)_{4}= 4 \times (-1)$ The overall charge is 0 on the complex, thus: $+1+x+0-4=0$ $+1+x-4=0$ $x=+4-1$ $x=+3$ The oxidation number of metal is +3