The oxidation state of chromium in the final product formed the reaction between $$K{\rm I}$$ and acidified potassium dichromate solution is :

On heating mixture of $$C{u_2}O$$ and $$C{u_2}S$$ will give :

Calomel $$\left( {H{g_2}C{l_2}} \right)$$ on reaction with ammonium hydroxide gives :

Pick out the isoelectronic structure from the following :

$$\eqalign{ & \left( i \right)\,\,\,\,\,\,C{H_3}^ + \cr & \left( {ii} \right)\,\,\,\,{H_3}{O^ + } \cr & \left( {iii} \right)\,\,\,N{H_3} \cr & \left( {iv} \right)\,\,\,\,C{H_3}^ - \cr} $$