Flame emission spectroscopy is used to identify metal ions in a firework. Figure 8 shows the flame emission spectra of five individual metal ions and a spectrum for a mixture of two metal ions. Which two metal ions are in the mixture? Select two options.

To identify the ions in the mixture, we need to find which individual spectra, when combined, create the mixture spectrum. Each line in an individual spectrum is like a fingerprint for that ion. - **Compare Li⁺ with the mixture:** The Li⁺ spectrum has lines at positions 100, 220, and 300-315. All of these lines are present in the mixture spectrum. So, Li⁺ is in the mixture. - **Compare Na⁺ with the mixture:** The Na⁺ spectrum has one thick line at position 260-270. This line is also present in the mixture spectrum. So, Na⁺ is in the mixture. - **Check the others:** The lines for Ca²⁺, Cu²⁺, and K⁺ do not match the lines seen in the mixture. Therefore, the mixture contains Li⁺ and Na⁺.