B-I
A Class A fire extinguisher is the least expensive and most easily available type of extinguisher to use on wood or paper fires. They are normally filled with water or water-based foam and pressurized with air.
Many different types of fire extinguishers exist and many different gases are used. A water extinguisher may contain pressurized air. Other types use carbon dioxide or compressed nitrogen. There are also halogenated extinguishers containing proprietary mixtures of fire-suppression gases.
It is the propellant used to force water out of the extinguisher.
Trick question, if the fire extinguisher is full of water, such as a Class 2A. However, a fire extinguisher is designed to put out a small fire quicker than anyone can respond with a hose and a water supply. Unfortunately, many fires react violently when water is applied to them, so a different type of fire extinguisher must be used.
In 1881, Almon M Granger patented a fire extinguisher which used the reaction between sodium bicarbonate and sulfuric acid to expel pressurized water. When the acid and bicarbonate mixed, carbon dioxide gas was released - which pressurized the water. These were still reasonably common up until the 1920s, but are not one of the common types of fire extinguishers used today.
The carbon dioxide fire extinguisher can be used on electrical fires, where there is a danger of an electrical shock if a soda water extinguisher was used.
A water-type or water-based foam type of extinguisher should not be used on an electrical fire because water and foam are electrical conductors and could result in electrocution of the person using the extinguisher or anyone stepping in the water.
What 'type' the fire is. The right extinguisher must be used for any fire. Or, more importantly - it can be very dangerous to use the wrong type of extinguisher, such as one with water should never be used on an electrical fire.
A water-type or water-based foam type of extinguisher should not be used on an electrical fire because water and foam are electrical conductors and could result in electrocution of the person using the extinguisher or anyone stepping in the water.
A soda water extinguisher can be used on a fire of paper. Or use a carbon dioxide extinguisher if you don't want water damage, or if there is anything electrical that can cause a shock. Use foam on oils and flammable liquids.
You need to use a Class B extinguisher on flammable liquids.