When an anhydrous sodium halide, NaX\text{NaX}NaX, reacts with concentrated sulfuric acid, a toxic gas with a characteristic rotten egg smell is evolved along with other products.
Which option correctly identifies the halide ion, X−\text{X}^-X−, and the change in the oxidation state of sulfur during the redox reaction that produces this specific gas?
Halide ion: Br−\text{Br}^-Br−; change in sulfur oxidation state: +6→+4+6 \rightarrow +4+6→+4
Halide ion: I−\text{I}^-I−; change in sulfur oxidation state: +6→−2+6 \rightarrow -2+6→−2
Halide ion: I−\text{I}^-I−; change in sulfur oxidation state: +6→0+6 \rightarrow 0+6→0
Halide ion: Br−\text{Br}^-Br−; change in sulfur oxidation state: +6→−2+6 \rightarrow -2+6→−2
106 exam-style questions on Edexcel GCSE Chemistry 7.2 Group 7, covering 7.2.1 Physical properties of the halogens, 7.2.2 Reactions of the halogens, 7.2.3 Relative reactivity and displacement reactions of the halogens, and 7.2.4 Halogen displacement as a redox reaction. Each one has a worked solution and a mark scheme showing where the marks go.