UPSC Prelims 2014 Question:

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:

Explanation:

• A chemical change is a process in which one or more substances are altered into one or more new and different substances. In other words, a chemical change is a chemical reaction involving the rearrangement of atoms.
  
  
• While a physical change can often be reversed, a chemical change typically cannot be, except through more chemical reactions. Crystallization of sodium chloride and melting of ice can be reversed, hence these are physical changes. So, point 1 and 2 are not correct.
  
  
• Souring of milk involves change of atoms, and typically cannot be reversed. Which is why it's a chemical change. So, point 3 is correct.
  
  

Therefore, option (2) is the correct answer. 

Subject: Science & Technology | Chemistry