Question

In which of the following does the central atom exhibit an oxidation state of +2 ?

• A. K2 [Ni(CN)4 ]
• B. K3 [Fe(CN)6]
• C. [Fe(C2O4)3 ]3-
• D. [Cu(NH3)4 ]2+

Answer 1

Answer: (A), (D)

K2 [Ni(CN)4 ]

Answer 2

K2(Ni(CN)4):
In this the anion will have a charge of -2 as 2K+ is present.

Then the charge on the central atom that is Ni can be calculated:
CN has a charge of -1, therefore Nickel x
x+4(-1) = -2
x = +2

[Cu(NH3)4 ]2+:
In this NH3 is neutral thus has a charge of 0 and the compound has an overall charge of +2.
Therefore the charge on the central atom that is Cu is +2.