Question
The oxidation states of $$Cr$$ in $$\left[ {Cr{{\left( {{H_2}O} \right)}_6}} \right]C{l_3},\left[ {Cr{{\left( {{C_6}{H_6}} \right)}_2}} \right]$$ and $${K_2}\left[ {Cr{{\left( {CN} \right)}_2}{{\left( O \right)}_2}{{\left( O \right)}_2}\left( {N{H_3}} \right)} \right]$$ respectively are :
A.
$$ + 3, + 4,\,{\text{and}}\, + 6$$
B.
$$ + 3, + 2,\,{\text{and}}\, + 4$$
C.
$$ + 3,0,\,{\text{and}}\, + 6$$
D.
$$ + 3,0,\,{\text{and}}\, + 4$$
Answer :
$$ + 3,0,\,{\text{and}}\, + 6$$
Solution :
$$\left[ {Cr{{\left( {{H_2}O} \right)}_6}} \right]C{l_3}$$
$$ \Rightarrow x + 6 \times 0 + \left( { - 1} \right) \times 3 = 0$$
$$ \Rightarrow x = + 3$$
$$\left[ {Cr{{\left( {{C_6}{H_6}} \right)}_2}} \right]$$
$$x + 2 \times 0 = 0;x = 0$$
$${K_2}\left[ {Cr{{\left( {CN} \right)}_2}{{\left( O \right)}_2}\left( {N{H_3}} \right)} \right]$$
$$2 \times 1 + x + 2 \times \left( { - 1} \right) + 2 \times \left( { - 2} \right) + \left( { - 2} \right) + 0 = 0$$
$$x = + 6$$