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.

A milkman adds a small amount of baking soda to fresh milk to shift the pH of fresh milk from 6 to slightly alkaline because alkaline conditions inhibit the growth of bacteria and help to preserve the freshness of milk. Baking soda (sodium bicarbonate) acts as a buffer, helping to maintain the pH of milk and prolong its shelf life.

Acids do not show acidic behavior in the absence of water because the characteristic properties of acids, such as the donation of hydrogen ions (H+) and the ability to react with bases, depend on the presence of water molecules to facilitate proton transfer reactions. In the absence of water, acids cannot ionize and exhibit their acidic properties.

Rainwater conducts electricity because it contains dissolved ions and gases from the atmosphere, such as carbon dioxide (CO2), oxygen (O2), and nitrogen oxides (NOx), which act as electrolytes and facilitate the flow of electric current. Distilled water, on the other hand, does not conduct electricity because it lacks dissolved ions and gases, making it a poor conductor of electricity.

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.