Correct Option
The correct option is Calcium hydroxide
Explanation
Whitewashing involves the application of a lime-based solution to walls. The process begins with Quick lime (Cal, which reacts vigorously with water to form Slaked lime (Calcium hydroxide, Ca(OH)2). This reaction is highly exothermic. The resulting aqueous solution of calcium hydroxide is the substance actually applied to the walls during whitewashing.
Analysis of Chemical Process
- Solution Preparation: When calcium oxide is mixed with water, it forms calcium hydroxide. Therefore, the solution in the bucket used for whitewashing contains Calcium hydroxide.
- Post-Application Reaction: After the calcium hydroxide solution is applied to the walls, it reacts slowly with carbon dioxide (CO2) present in the air. This reaction forms a thin layer of Calcium carbonate (CaCO3) over a period of two to three days, which provides the characteristic shiny white finish.
Option Analysis
- Calcium hydroxide Calcium hydroxide: Correct. This is the chemical compound present in the aqueous solution (slaked lime) used for application.
- Calcium oxide Calcium oxide: Incorrect. This is the raw material (quick lime) used to prepare the solution, not the compound present in the solution itself.
- Calcium carbonate Calcium carbonate: Incorrect. This is the solid product formed on the wall after the whitewash dries and reacts with air; it is not the solution used for application.
- Gypsum Gypsum: Incorrect. Gypsum (CaSO4·2H2O) is used in the production of Plaster of Paris and cement, not in whitewashing solutions.
Key Takeaway: The solution used for whitewashing is Slaked Lime (Calcium hydroxide). The shiny white finish obtained days later is due to the formation of Calcium carbonate.