Question 45 from UPSC CSE 2014 - Science and Technology

Question

Which of the following is/are 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.

IASCODEX · Accepted Answer

Correct Option: B. 3 only

Strategy: Distinguish between physical and chemical changes by identifying whether the process forms new substances. Crystallization and melting only alter the state or arrangement, not the composition. Souring of milk, however, produces new substances through chemical reaction, confirming it as a chemical change.

Key Info: A chemical change involves a transformation where original substances form new substances with different chemical properties. These changes are often irreversible. A physical change alters the state or arrangement of a substance without changing its chemical composition and is typically reversible.

**Examples of Chemical Change**
- Rusting
- Burning
- Digestion
- Fermentation
- Souring of milk, caused by the fermentation of lactose into lactic acid by bacteria.

**Examples of Physical Change**
- Sublimation
- Evaporation
- Freezing
- Boiling
- Dissolving solids
- Crystallization of sodium chloride, which forms solid crystals from a solution without changing its chemical identity (NaCl).
- Melting of ice, which is the transition of water from solid to liquid without altering its molecular structure (H2O).

IASCODEX · Answer

Option A: 1 and 2 only

IASCODEX · Answer

Option C: 1, 2, and 3

IASCODEX · Answer

Option D: None of the above

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

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

Crystallization of sodium chloride

Melting of ice

Souring of milk
Select the correct answer using the code given below.