Which of the following compounds will be suitable for Kjeldahl’s method for nitrogen estimation?

Consider the following reaction and statements:
[Co(NH₃)₄Br₂]⁺ + Br^- $$\to$$ [Co(NH₃)₃Br₃] + NH₃
(I) Two isomers are produced if the reactant complex ion is a cis-isomer
(II) Two isomers are produced if the reactant complex ion is a trans-isomer
(III) Only one isomer is produced if the reactant complex ion is a trans-isomer
(IV) Only one isomer is produced if the reactant complex ion is a cis – isomer
The correct statements are

The compound that does not produce nitrogen gas by the thermal decomposition is :

The oxidation states of Cr in [Cr(H₂O)₆]Cl₃, [Cr(C₆H₆)₂] and K₂[Cr(CN)₂(O)₂(O₂)(NH₃)] respectively are :