Flame test of Li and Sr
You cant differentiate the 2 using a flame test. You must use other chemical reactions I’ll give an example If your solution contains only Li+ or Sr2+, you can differentiate them by adding a sulfate solution (for example, Na2SO4 or diluted sulfuric acid). If strontium is present, a white, fine-crystalline precipitate of SrSO4 will form. In the case of lithium, the solution will remain clear. This is because SrSO4 is much less soluble in water than Li2SO4.