In [Pt(en)₂CI₂] the charge on the complex ion is +2 and coordination number is 6. Hence, the primary and secondary valency are +2 and 6 respectively.

Let the oxidation state of pt be x.
Oxidation state of cl is -1.
So x + 0 – (1*3) must be equal to -1 since the charge of the whole compound is -1.
x + 0 – (1*3) = -1
x -3 = -1
x = -1 + 3
x = +2
So the oxidation state of platinum is +2.
Secondary is due to legend there are mono deadened legend 
then 1×4= 4
 

Pt(NH₃)₂CI₄] is neutral complex and no ions are formed in aqueous solution.

K,(PtCl₆] → 2K⁺ + [PtCI₆]^2-
It does not have Cl^- ion toffive precipitate of AgCI.

Total chlorine molecules are 3 and one third means one chlorine molecule precipitates. So, one chlorine has to be outside the coordination sphere and that is in option C.

Mohr's salt is a doub le salt and it will give test for Fe²⁺ ion. It dissociates into simple substances or ions completely when dissolved in water.

Cr(24) = [Ar]3d54s1
Since (CO) is strong ligand, in Cr(CO)6 none of the electron is unpaired. Therefore ‘spin only’ magnetic moment is zero.

The acetylacetonate (acac) forms six membered ring as follows:

Correct Answer : a

Explanation : NO in brown ring complex has +1 oxidation state.

Let oxidation state of Fe be x.

Since the overall charge on the coordination sphere, [Fe(H2O)5NO+]  is +2, the sum of oxidation states of all elements in it should be equal to +2.

Therefore, x+1=+2

or, x=+1 

Hence, the oxidation state of iron in the brown ring complex is +1.

[Fe(H2O)5NO+]2- iron is assigned an oxidation state of 2+. The iron center has a diamagnetic low-spin d6 electron configuration, although a paramagnetic long-lived metastable state has been observed by EPR spectroscopy. The chemical reactions of sodium nitroprusside are mainly associated with the NO ligand.

In [Ni(CO)₄]
Let the oxidation state of Ni is x.
x + 4 x (0) = 0 (Carbonyl (CO) is a neutral ligand and have zero charge.)
x = 0
Hence, Ni have zero oxidation state.

CH₃COCH₂COCH₃

It can ligate through two oxygen atoms.