# What is the oxidation number of the transition metal in the complex ion [Co(H$_2$O)$_5$Cl]$^{+}$?

$(a)\;+3\qquad(b)\;+4\qquad(c)\;+7\qquad(d)\;+2$

The complex ion has an overall positive charge of +1.
It has 5 neutral H$_2$O ligands with no charge and one Cl ion with a -1 charge.
Therefore the oxidation state for Co is $= +1 - (-1) = +2$
edited Aug 4, 2014