Which one of the following halogens turn(s) starch iodide paper blue?
Chlorine turns moist starch iodide paper blue-black because the iodide ions on the paper are oxidised to iodine and the starch react to it to give blue-black compound.
The bromine releases iodine from the potassium iodide. Iodine reacts with starch to produce a blue color.
Br2+2KI → 2KBr+I2