The correct answer is (a) Sodium hydrogen carbonate, also known as baking soda.
Sodium hydrogen carbonate is a white, water-soluble solid that is used in a variety of applications, including fire extinguishers. When sodium hydrogen carbonate is mixed with water, it produces carbon dioxide gas. This gas helps to smother the fire by displacing the oxygen that the fire needs to burn.
Sodium hydrogen carbonate is also a relatively safe substance to use. It is not flammable and does not produce toxic fumes when it is heated. This makes it a good choice for use in fire extinguishers that are used in areas where there are people or animals present.
The other options are incorrect because they are not used in fire extinguishers. Sodium hydrogen sulphate is a white, water-soluble solid that is used in a variety of applications, including as a desiccant and as a mordant in dyeing. Sodium carbonate is a white, water-soluble solid that is used in a variety of applications, including as a cleaning agent and as a water softener. Sodium sulphate is a white, water-soluble solid that is used in a variety of applications, including as a fertilizer and as a desiccant.