Answer: option 3) magnesioum reacts with an acid.
Justification:
1) Malleability, conduction of electricity, and boiling point are physical properties.
2) Maleability is the ability to be transformed into foil. It is just a change in form. So, it is a physical property.
3) The metals conduct electricity in virtue of the array of the atoms, which permtis the flow of the electrons, but it does not involve a chemical change, so it remains being a physical proerty.
4) Boling point is the temperature at which a substance passes from liquid state to gas state, which are just different forms of the same substance. So, it is other physical property.
5) Reaction with an acid is indeed a chemical transformation: the metal (magnessium) will form a chemical bond with some spieces of the acid to form a new compound. This is a chemical reaction in virtue of the chemcial properties of the substance (its ability to react with acids)