Answer is: formula of the complex is [Cr(NH₃)₂(SCN)₄<span>]</span>⁻<span>. This complex has negative charge (-1) because chromium (central atom or metal) has oxidation number +3, first ligand ammonia has neutral charge and second ligand thiocyanate has negative oxidation number -1: +3 + 2</span>·0 + 4·(-1) = -1.
