Which physical property of iron made it popular for use in
1. magnetism
2. luster
3. malleability
4. ductility

Option (3) is the correct answer.

Explanation:

Iron is a metal and it is known that metals are malleable, that is, they can be drawn into sheet. Also, metals are ductile in nature, that is, they can be changed into thin wires.

Therefore, weapons like sword, ax etc are the weapons which have malleable surface.

Whereas magnetism is a property in which a weapon is attracted by a magnet. Luster is a property which shows shiny surface of a metal.

Therefore, we can conclude that malleability is a physical property of iron which made it popular for use in weapons.