Common Chemical Compounds and Reactions

Soda ash is the common name for anhydrous sodium carbonate, Na2CO3. Option A is baking soda (sodium bicarbonate), option B is washing crystals (hydrated sodium carbonate), and option C is caustic soda (sodium hydroxide).

CaCl2 is an excellent desiccant due to its high hygroscopicity - it readily absorbs water vapor from the air to form hydrated species. Na2CO3 can absorb some water but is less effective, NaCl is not hygroscopic enough, and Na2SO4 is used as a drying agent only after initial drying, not as a primary desiccator.

Potash alum is KAl(SO4)2·12H2O, a double sulfate containing potassium and aluminum in 1:1 ratio with 12 water molecules. Option B shows 2:1 stoichiometry with 24 waters, option C shows 2:1 with 6 waters - neither matches the correct formula of common potash alum.

Chalk powder is insoluble in water. Out of salt, sugar and baking powder, salt particles are the smallest in size and thus, get dissolved the fastest in water. 

Pearls are composed primarily of calcium carbonate (CaCO3) in the form of aragonite crystals, layered with conchiolin (an organic protein) to create the characteristic nacre structure. This combination gives pearls their luster and iridescence.

Gypsum is a very soft sulphate mineral composed of calcium sulphate dihydrate, with the chemical formula CaSO_4•2H₂O. Lithopone is a white pigment consisting of a mixture of barium sulphate (BaSO₄) and zinc sulphide (ZnS). Lithopone is a white pigment consisting of a mixture of barium sulphate (BaSO₄) and zinc sulphide (ZnS). Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H₂Mg₃(SiO₃)₄ or Mg₃Si₄O₁₀(OH)₂.

Camphor has the property of sublimation. Thus, even at room temperature it evaporates.

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.