Describe the use of NPK fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth

Describe the use of a flame test to identify the cations: (a) lithium, ( Li^+ ) (b) sodium, ( Na^+ ) (c) potassium, ( K^+ ) (d) calcium, ( Ca^{2+} ) (e) barium, ( Ba^{2+} ) (f) copper(II), ( Cu^{2+} )