Which of the following is/are the example/examples of chemical change?

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.

1 and 2 only
3 only
1, 2 and 3
None
This question was previously asked in
UPSC IAS – 2014
The correct answer is B) 3 only. A chemical change results in the formation of new substances with different properties, while a physical change only alters the form or appearance of a substance, but not its chemical composition.
1. Crystallization of sodium chloride: This is a process where dissolved salt precipitates out of a solution as crystals. It is a physical change because the chemical composition (NaCl) remains the same.
2. Melting of ice: This is a change of state from solid water (ice) to liquid water. It is a physical change because the substance is still water (H₂O), just in a different form.
3. Souring of milk: This occurs when bacteria convert lactose (milk sugar) into lactic acid. This process creates new chemical substances (lactic acid) and changes the milk’s properties (taste, smell, texture). This is a chemical change.
Indicators of a chemical change often include the formation of a gas, a change in color, a change in temperature, the formation of a precipitate, or the production of light or sound. Souring of milk is a form of fermentation, a biochemical process leading to chemical transformation.