Which statement correctly explains the violet colour of the complex ion \( [Cu(NH_3)_4(H_2O)_2]^{2+} \) formed when copper(II) sulfate reacts with an excess of ammonia?
Which statement correctly explains the violet colour of the complex ion \( [Cu(NH_3)_4(H_2O)_2]^{2+} \) formed when copper(II) sulfate reacts with an excess of ammonia?