Therefore, the oxidation number of chromium must be
the same as the charge of the complex  ion, +3 2 [Co(H2NCH2CH2NH2)3]2(SO4)3 is named as:
tris(ethane-1,2–diamine)cobalt(III) sulphate
Explanation: The sulphate is the counter anion in this molecule Since it takes 3 sulphates to bond with two complex cations, the
charge on each complex cation must be +3