Which of the following is a size reduction technique for solids?

• A. Stirring
• B. Grinding
• C. Decantation
• D. Filtration

Answer: (B)

Reducing the size of solid particles is achieved by applying mechanical forces that break larger pieces into smaller ones. Grinding does exactly this by using mills or grinders that apply friction, impact, and pressure to fracture solids into finer particles. This process increases surface area and often helps with dissolution, mixing, or subsequent reactions.

Stirring, on the other hand, is about mixing materials to improve homogeneity and mass transfer; it doesn’t break particles into smaller pieces. Decantation relies on gravity to separate liquids from solids or to separate immiscible liquids, not to reduce particle size. Filtration separates solids from liquids by passing a suspension through a filter; while it can remove some material, it does not reduce the size of the solid particles themselves.