Which of the following is/are the example/examples of chemical change? 1. Crystallization of sodium chloride 2. Melting of ice 3. Souring of milk Select the correct answer using the code given below.

Reference [1] gives the core criterion used to decide whether a process (like crystallization) is chemical or physical: formation of a new substance.

This is a high-yield definitional concept often used to classify processes in questions. Mastering it lets you quickly decide outcomes in lab and natural-process scenarios, and link to topics like reactions and separations. Practice by applying the criterion to several examples (dissolution, crystallization, combustion).

References [4] and [2] describe separating dissolved NaCl and formation of rock salt via drying/evaporation — a physical route to obtain solid salt.

Understanding common physical separation methods (evaporation, crystallization) is useful for questions on natural resource formation, laboratory techniques, and industrial processes. It links chemistry to earth science (e.g., rock salt beds) and is best learned by mapping process → outcome examples.

Reference [3] explains chemical formation of NaCl from elements (ionic bonding), while [4] shows crystallization of already-formed NaCl — helping separate chemical synthesis from physical phase change.

Helps answer trick questions that mix synthesis (chemical change) with recovery/separation (physical change). Useful across inorganic chemistry and materials questions; practice by contrasting formation reactions with recovery processes.

The core classification uses whether a new substance forms; references define physical and chemical changes directly.

High-yield for basic science/GS questions: knowing the defining criterion (new substance vs. only physical property change) helps classify processes (melting, rusting, combustion). Links to chemistry basics and simple experiments; learn definitions and apply them to examples.

References use ice melting/refreezing to illustrate reversibility as characteristic of many physical changes.

Frequently tested when distinguishing types of changes; helps quickly eliminate options in MCQs by asking if original material can be recovered. Practice by categorising common processes (evaporation, condensation, burning).

Melting is a state change (solid→liquid); melting points (e.g., ice at 0°C) are discussed and link to interparticle forces.

Useful for linking physical change concepts to material properties (melting point, interparticle forces) in both science and environment contexts (glaciers melting). Know typical examples and numerical melting points for conceptual questions.

Classification hinges on whether a new substance forms (explicitly defined in the references) and is applied to milk souring when lactic acid is produced.

High-yield foundational concept for basic chemistry questions: it lets candidates quickly classify processes (e.g., fermentation, rusting, melting). Mastering the definition and applying it to examples builds accuracy in both objective and descriptive answers; practice by mapping everyday examples to the 'new substance' test.