What can be determined from a flame emission line spectrum?

The flame emission line spectrum is a powerful analytical tool used primarily to identify the presence of metal ions in a sample and to determine their concentration. When a sample is heated in a flame, the metal ions absorb energy and become excited. As they return to their ground state, they emit light at specific wavelengths unique to each element. This emission produces a characteristic line spectrum, with each line corresponding to a different wavelength of light emitted by that particular metal ion.

By analyzing the spectrum, chemists can identify which metal ions are present based on the specific wavelengths observed. Additionally, the intensity of the emitted lines is directly related to the concentration of those ions in the sample; therefore, it can also provide a quantitative measurement of their concentration. This dual capability of identifying metal ions and determining their quantities is what makes option B the correct choice.

In contrast, the other options do not provide the same level of specificity or capability. While flame spectra do not directly provide information about the amount of gas present or the temperature of a sample, and determining the color of the sample alone does not yield any quantitative or qualitative information about the elements present, option B encompasses both identification and concentration determination, thus making it the most comprehensive answer.