Identify neutral ligand from following.

The charge of a ligand determines its contribution to the overall charge of a coordination complex. Nitrato ($\mathrm{NO^{3-}}$) has a -1 charge, cyano ($\mathrm{CN^-}$) has a -1 charge, and iodo ($\mathrm{I-}$) has a -1 charge. The aqua ligand ($\mathrm{H_2 O}$) is neutral with zero charge.

The neutral ligand is aqua.