Question

Oxidation number of the metals in each case are :

(a)$K_3\left[Fe\right(CN{)}_6]$ (b)$K_3\left[Cr\right(C_2{O}_4{)}_3]$

(c)$\left[Ni\right(CN{)}_4{]}^{2-}$ (d)$N{a}_{2}Mo{O}_4$

(e)$Fe(CO{)}_5$ (f)$MgW{O}_4$

• A. (a) +3 (b) +2 (c) +1 (d) +7 (e) +4 (f) +5
• B. (a) +3 (b) +3 (c) +2 (d) +6 (e) +0 (f) +6
• C. (a) +2 (b) +3 (c) +1 (d) +4 (e) +1 (f) +5
• D. None of these.

Answer 1

Answer: (B)

(a) +3 (b) +3 (c) +2 (d) +6 (e) +0 (f) +6

a) $K_3\left[Fe\right(CN{)}_6]$ Oxidation number is 1 (+3)+x-6(-1) = 0,i.e x = 6-3 i.e +3

b) $K_3\left[Cr\right(C_2{O}_4{)}_3]$ Oxidation number is 3(+1)+x-3(-2) = 0,i.e x = 6-3 i.e +3

c) $\left[Ni\right(CN{)}_4{]}^{2-}$ Oxidation number is x-4+2 = 0,i.e x = 4-2 i.e +2

d) $N{a}_{2}Mo{O}_4$ oxidation number is 2(+1)+ x - 4(-2) = 0,i.e x = 8-2 i.e +6

e) $Fe(CO{)}_5$ oxidation state of Fe in $Fe(CO{)}_5$ is 0 because CO is a neutral ligand and does not contribute to charge so Fe is in its neutral state with oxidation number = 0

f) $MgW{O}_4$ Oxidation number is 1(+2)+x-4(-2) = 0,i.e x = 8-2 i.e +6

Hence option B is correct.