The correct answer is option 3: 1, 2, and 3.

To better understand why these options are not chemical changes, let`s dissect each one:

1. Tempering of iron: Tempering involves heating and cooling iron to improve its hardness and toughness. It does not involve a chemical reaction, but rather a physical change in the arrangement of the iron`s atoms.

2. Conversion of iron piece into an electro-magnet by passing the current around the iron: This process is known as electromagnetism, where the passage of electric current generates a magnetic field around the iron. It is also a physical change and does not involve any chemical reactions.

3. Melting of iron: Melting involves applying heat to change a solid into a liquid. In this case, iron changes from a solid state to a liquid state, but no chemical reactions occur. It is purely a physical change.

4. Rusting of iron: Alert - correct answer should be option 2: 3 and 4 only. Rusting is a chemical change that occurs when iron reacts with oxygen and water in the presence of moisture, resulting in the formation of iron oxide. This is a prime example of a chemical change.