Which group 7 ion produces a yellow result in tests?

The ion that produces a yellow result in tests is iodide. This is due to the properties of iodine, particularly when it forms a complex with certain reagents or under specific conditions. For example, when iodide ions are treated with starch, they can produce a blue-black coloration due to the formation of a starch-iodine complex. However, in other contexts, such as in precipitation reactions involving heavy metal cations, the resulting precipitate containing iodine can appear yellow.

Chloride, bromide, and fluoride ions typically do not display yellow coloring in standard tests. Chloride ions produce white precipitates when reacting with silver nitrate, while bromide may yield a cream-colored precipitate. Fluoride, on the other hand, does not produce any distinct color changes in standard tests. Overall, the distinctive yellow or dark coloration associated with iodide is what makes it the correct choice in this context.