Which gas is evolved when concentrated HCl is added to powdered potassium dichromate. On passing the evolved gas through acidified KBr solution, the solution turns brown. Write the balanced equations for the reactions involved.

Explanation

Due to its great reactivity white or yellow phosphorus is always kept under water. In air, white or yellow phosphorus is spontaneously oxidised to `P_2 O_3` and `P_2 O_5` even at room temperature.