Identify anionic ligand from following.

The anionic ligand is identified by analyzing the charge characteristics of each option.

A) Isothiocyanato ($\text{SCN}^-$) carries a negative charge.

B) Ammine ($\text{NH}_3$) is neutral.

C) Aqua ($\text{H}_2\text{O}$) is neutral.

D) Ethylenediamine ($\text{H}_2\text{N-CH}_2\text{-CH}_2\text{-NH}_2$) is neutral.

Since only isothiocyanato possesses an anionic character, the correct choice is $\boxed{\text{A}}$.