A soda acid extinguisher works by mixing sulphuric acid with a solution of baking soda, sodium bicarbonate — option 3.

How the device is built. The body of the cylinder holds the sodium bicarbonate solution, and the acid is sealed separately in a small glass bottle inside it. Striking the knob breaks the bottle, the two mix, and carbon dioxide is released at once :

\(2\text{NaHCO}_{3}+\text{H}_{2}\text{SO}_{4}\rightarrow\text{Na}_{2}\text{SO}_{4}+2\text{H}_{2}\text{O}+2\text{CO}_{2}\uparrow\)

The gas builds up pressure inside the sealed cylinder, which forces the liquid out through the nozzle in a jet, and the same gas smothers the flames when it arrives.

Why carbon dioxide puts a fire out. It does two things at once. It is about one and a half times as dense as air, so it settles over the burning material and cuts off the supply of oxygen; and it will not itself burn, so it cannot feed the fire. A fire needs fuel, heat and oxygen together, and removing any one of the three ends it — this attacks the oxygen.

The word “soda” is the key. Here it means baking soda, sodium hydrogen carbonate, NaHCO₃. Washing soda, sodium carbonate, is a different compound, and the two options naming it are there precisely to catch a candidate who does not separate the two. Both would in fact give off carbon dioxide with an acid, so the distinction is one of what the extinguisher is actually charged with rather than of chemistry.

Where it must not be used. The discharge is a water-based solution and conducts electricity, so a soda acid extinguisher is unsafe on live electrical equipment, and on burning oil the water simply spreads the fire. Carbon dioxide or dry powder extinguishers are used in those cases.

Hence, the answer is sulphuric acid and sodium bicarbonate solution.