The Soda-acid fire extinguisher contains

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sulphuric acid and solution of sodium hydrogencarbonate

nitric acid and solution of sodium hydrogencarbonate

sulphuric acid and solution of sodium carbonate

sulphuric acid and solution of potassium carbonate

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UPSC CAPF – 2019

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The correct option is A.

A soda-acid fire extinguisher operates based on the chemical reaction between an acid and a carbonate or bicarbonate to produce carbon dioxide gas. The standard composition of a soda-acid fire extinguisher involves sulphuric acid (H₂SO₄) and a solution of sodium hydrogencarbonate (sodium bicarbonate, NaHCO₃). When the extinguisher is activated (typically by inverting it or breaking a capsule), the acid mixes with the bicarbonate solution, leading to the reaction: H₂SO₄ + 2NaHCO₃ → Na₂SO₄ + 2H₂O + 2CO₂. The released CO₂ gas builds pressure, expelling the solution and also acts as a smothering agent to cut off oxygen supply to the fire.

Soda-acid fire extinguishers are effective against Class A fires (combustible materials like wood, paper, textiles) but are not suitable for Class B (flammable liquids), Class C (flammable gases), or Class D (metals) fires, especially not for electrical fires due to the water content. Modern fire extinguishers often use different agents like dry chemical powders, foam, or CO₂ directly.

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