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.
Answer & explanation
Answer: (b) 3 only
A chemical change makes a new substance. Crystallisation of salt and melting of ice only change the form or state of the same substance. Souring of milk is caused by bacteria turning milk sugar into acid, so a new substance forms. Only statement 3 describes a chemical change, so the answer is (b).
- ✗ 1. Crystallisation of sodium chloride from its solution only brings the same NaCl out as solid crystals. No new substance forms, so it is a physical change.
- ✗ 2. Ice melting into water is a change of state. Water stays water (H2O), so this is a physical change.
- ✓ 3. Lactic acid bacteria grow in milk and make acids. The acids coagulate the milk proteins, so the milk curdles and its taste and properties change. New substances form, so this is a chemical change.
Remember · Physical change: only shape, size or state alters and no new substance forms (melting, crystallisation, dissolving). Chemical change: new substances form (souring, curdling, rusting, burning, cooking).
📘 Read it in NCERT: Class 7 Curiosity, Ch 5 (practise this chapter) · Class 7 Curiosity, Ch 5 (practise this chapter) · Class 12 Biology, Ch 8 (practise this chapter)
Sources
- NCERT Class 7 · Curiosity, Chapter 5 “Such changes in which only physical properties like shape, size, and state of substances change are called physical changes.”
- NCERT Class 7 · Curiosity, Chapter 5 “A chemical change is one in which one or more new substances are formed.”
- NCERT Class 12 · Biology, Chapter 8 “During growth, the LAB produce acids that coagulate and partially digest the milk proteins.”
Question: UPSC Civil Services (Preliminary) 2014, General Studies Paper I. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·
