The formula of ‘nitrosyl’ group
 

It is given to find out the formula of the ‘nitrosyl’ group. 

Explanation

Metal nitrosyl complexes are complexes in which nitric oxide, NO, is connected to a transition metal. 

Most complexes having NO ligands are derived from the nitrosyl cation,${\mathrm{NO}}^{+}$.
The nitrosyl cation has the same no. of electrons as carbon monoxide. 
The metal-nitrosyl ligand in nitrosyl complexes has a linear structure. The nitrosyl cation donates two electrons to the metal and gains electrons from the metal through back-bonding. 

Here the answer is B) ${\mathrm{NO}}^{+}$.