Which one of the following compounds is used as a chemical in certain type of fire extinguishers

We need to identify which compound is used as a chemical in certain types of fire extinguishers. Let us examine each option:

Option A: Washing soda ($$Na_2CO_3 \cdot 10H_2O$$) - Used in cleaning and water softening, not in fire extinguishers.

Option B: Baking soda ($$NaHCO_3$$) - Sodium bicarbonate is used in soda-acid type fire extinguishers. When heated or mixed with acid, it decomposes as: $$2NaHCO_3 \to Na_2CO_3 + H_2O + CO_2$$. The $$CO_2$$ gas released helps extinguish the fire by cutting off the oxygen supply.

Option C: Caustic soda ($$NaOH$$) - Used in soap making and industrial processes, not in fire extinguishers.

Option D: Soda ash ($$Na_2CO_3$$) - Anhydrous washing soda, used in glass manufacturing, not in fire extinguishers.

The correct answer is Option B: Baking soda.