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}