Explanation: Gypsum is a naturally occurring mineral that is widely used in construction, particularly for plastering buildings. It is a soft sulfate mineral with the chemical formula CaSO₄·2H₂O, which means it contains calcium, sulfur, oxygen, and water. Gypsum is known for its binding properties and its ability to form a paste when mixed with water, which hardens into a solid material when dried.
The use of gypsum for plastering is based on its unique properties. When gypsum is mixed with water, it undergoes a chemical reaction called hydration, during which the water molecules react with the gypsum crystals to form a new crystalline structure. This process is reversible, meaning that the hardened gypsum can be rehydrated and reused, making it a sustainable material.
Gypsum plaster is applied to walls and ceilings in a wet state, and as it dries, it forms a smooth, durable surface. The plaster can be sanded to achieve a smooth finish and can be painted or decorated as desired. Gypsum is also fire-resistant and has good sound insulation properties, making it a popular choice for interior finishes.
In contrast, the other options listed are not suitable for plastering. Mica is a mineral that is used for insulation and decorative purposes, but it does not bind well and cannot form a cohesive layer when applied to walls. Limestone, while used in construction, is too hard and does not form a workable paste when mixed with water. Copper is a metal and is not used for plastering because it does not have the necessary binding properties.
In summary, gypsum is the correct material for plastering buildings due to its binding properties, ease of application, and the smooth, durable surface it creates when dried. Its unique chemical properties make it an ideal choice for interior finishes in construction.