Common Chemical Compounds and Reactions

Correct Answer: Sodium thiosulphate

  Option 2 is the correct answer.

Washing soda is a chemical compound that can be used to remove stubborn stains.

Lead nitrate decomposes on heating to form lead oxide (yellow), nitrogen dioxide (brown gas), and oxygen - a clear chemical change. Sodium chloride, silica, and platinum wire are thermally stable and do not undergo chemical reactions when heated in air. The decomposition of lead nitrate is a classic example of thermal decomposition.

Baking powder is a leavening agent containing sodium bicarbonate (baking soda) as its primary active ingredient. When moistened, the sodium bicarbonate reacts with acid components to produce carbon dioxide gas, which makes baked goods rise. Sodium carbonate is washing soda, silicon carbide is an abrasive, and calcium oxide is quicklime - none are used in baking powder.

Hard water contains dissolved calcium and magnesium ions (usually as sulfates, chlorides, or bicarbonates) that interfere with soap's cleaning action. Soft water has little or no dissolved calcium/magnesium. Heavy water contains deuterium oxide (D2O) and is used in nuclear reactors. Mineral water contains dissolved minerals but may or may not be 'hard'.

Marble is a metamorphic rock formed from limestone, composed primarily of calcium carbonate (CaCO3). This gives marble its characteristic properties and reaction with acids.

Option (1) is the correct answer.

Bleaching powder (calcium hypochlorite) is obtained by the interaction of chlorine with a dilute solution of calcium hydroxide (slaked lime). The reaction produces Ca(OCl)Cl which acts as the bleaching agent.

 Option (2) is the correct answer.

Baking soda is the common name for sodium bicarbonate (NaHCO3), a white crystalline compound. It is used in baking as a leavening agent because it reacts with acids (like cream of tartar or buttermilk) to produce carbon dioxide gas, which makes baked goods rise. Sodium carbonate (washing soda) is a different compound. Sodium nitrate and potassium nitrate are used in fertilizers and food preservation.

Sodium benzoate is a widely used food preservative that inhibits the growth of bacteria, yeasts, and molds in acidic foods and beverages. It is particularly effective in soft drinks, pickles, and sauces. Sodium carbonate and bicarbonate are not preservatives; sodium thiosulphate is used in photography and medicine.