When a lot of dry powder of a substance X is released over a fire, the fire gets extinguished.

(a) Sodiumbicarbonate (sodiumhydrogencarbonate)
(b) The heat of fire decomposes sodium bicarbonate to produce carbondioxide gas. This carbon dioxide covers the fire like a blanket and cuts off supply of fresh air to the burning substance. Due to this the fire gets extinguished
(c) Potassium bicarbonate(or Potassium hydrogen carbonate)