Plaster of Paris is stored in a moisture-proof container because it is highly hygroscopic, meaning it readily absorbs moisture from the atmosphere. Exposure to moisture can cause Plaster of Paris to undergo premature setting or hardening, rendering it unusable. Storing it in a moisture-proof container helps to maintain its dryness and extend its shelf life.

Neutralization reaction is a chemical reaction in which an acid reacts with a base to form a salt and water. Two examples of neutralization reactions are:

• Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)
• Sulfuric acid (H2SO4) + Calcium hydroxide (Ca(OH)2) → Calcium sulfate (CaSO4) + Water (H2O)

Two uses of baking soda are:

• Baking soda (sodium bicarbonate, NaHCO3) is used as a leavening agent in baking to help dough rise.
• It is used as an antacid to relieve heartburn, indigestion, and upset stomach by neutralizing excess stomach acid.

Two uses of washing soda (sodium carbonate, Na2CO3) are:

• Washing soda is used as a cleaning agent and laundry detergent booster due to its alkaline properties, which help to remove stains and grease.
• It is used in water treatment processes to soften hard water by precipitating calcium and magnesium ions.

Sour substances contain acidic compounds that can react with copper and brass to form toxic compounds such as copper acetate or copper sulfate. These compounds can leach into the food or drink stored in the vessels, posing health risks. Therefore, it is not advisable to keep sour substances in brass and copper vessels.