UPSC CSE Prelims
Question 29
Which of the following is/are the example/examples of chemical change?
- Crystallization of sodium chloride
- Melting of ice
- Souring of milk
Select the correct answer using the code given below.
View correct answer and explanation
Correct answer: B
Correct Option: B
Explanation: Only souring of milk is a chemical change because bacterial fermentation generates new substances, notably lactic acid.
Statement/Pair-wise Analysis:
Statement/Item 1: Incorrect - Salt crystallization changes physical arrangement, not chemical identity.
Statement/Item 2: Incorrect - Melting ice is a reversible change of state of water.
Statement/Item 3: Correct - Lactose fermentation forms lactic acid and changes milk chemically.
Option-wise Analysis:
A: Incorrect - includes incorrect statement/items 1, 2; omits correct statement/item 3.
B: Correct - includes all and only the correct items.
C: Incorrect - includes incorrect statement/items 1, 2.
D: Incorrect - omits correct statement/item 3.