`MnO_(2)` oxidizes halide ions into dihalogen Reducing nature of halide ions follow the order, `F^(-) lt CI^(-) lt Br^(-) lt I^(-)` Y' gas may be `I_(2)`, which turns KI-strach paper into blue colour. Y' gas may be `CI_(2)` and `Br_(2)` which oxidises `KI` to `I_(2)` and turns strach paper blue.