Which of the following are not chemical changes ?
1. Tempering of iron
2. Conversion of iron piece into an electro-magnet by passing the current around the iron
3. Melting of iron
4. Rusting of iron
Select the correct answer using the code given below :
1 and 2 only
3 and 4 only
1, 2 and 3
1, 3 and 4
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CAPF – 2014
1. Tempering of iron: This is a heat treatment process that changes the microstructure and properties (like hardness and toughness) of iron alloys (steel). While it involves heat, it primarily changes the physical state and crystalline structure, not the fundamental chemical composition of the iron or steel. It is considered a physical process.
2. Conversion of iron piece into an electro-magnet by passing the current: When electric current passes around an iron core, it becomes a temporary magnet. This is a physical phenomenon (magnetism) induced by the electric current. The iron itself does not undergo a chemical transformation.
3. Melting of iron: This is a change of state from solid to liquid. The chemical composition of iron remains Fe. This is a physical change.
4. Rusting of iron: Iron reacts with oxygen and water to form hydrated iron(III) oxides (rust, typically Fe2O3.nH2O). This is a chemical reaction that produces new substances with different chemical properties than iron. This is a chemical change.
The question asks which are *not* chemical changes. These are the physical changes: 1 (Tempering), 2 (Electromagnetism), and 3 (Melting).