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 :

A physical change involves changes in physical properties without forming new substances, whereas a chemical change results in new chemical identities [5]. Melting of iron is a physical change because it is a change of state (solid to liquid) without altering the chemical composition of iron [5]. Conversion of iron into an electromagnet is also a physical change; it involves the magnetic effect of electric current where the iron core gains magnetic properties temporarily without any chemical reaction [4]. Tempering of iron is a heat treatment process that alters the microstructure and physical properties (like hardness and ductility) of the metal through controlled heating and cooling, but it does not change the chemical identity of the iron itself. In contrast, rusting of iron is a chemical change because it involves a reaction with moisture and oxygen to form a new substance, iron oxide [5]. Therefore, 1, 2, and 3 are not chemical changes.

Sources

1. [5] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > In a Nutshell > p. 68
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.5.1 Prevention of Corrosion > p. 54
3. [4] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 4: Electricity: Magnetic and Heating Effects > Snapshots > p. 58
4. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > 5.3.1 Rusting > p. 62
5. [3] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > 1.3.1 Corrosion > p. 13