An electric iron uses a heating element made of an alloy instead of pure metal. Which property of alloys justifies this choice?

The correct option is Alloys have higher resistivity and do not oxidise readily at high temperatures.

An electric iron is a heating appliance that works on the principle of the heating effect of electric current. According to Joule's law of heating, the heat produced ($H$) in a resistor is directly proportional to its electrical resistance ($R$) for a given current and time, as represented by the formula:

$H=I^{2}Rt$

To produce a large amount of heat, the heating element must have a high resistance. Since resistance is directly proportional to resistivity ($\rho$), using a material with high resistivity helps generate sufficient heat.

Alloys (such as Nichrome, which is an alloy of nickel, chromium, manganese, and iron) possess significantly higher resistivity compared to their constituent pure metals. This high resistivity allows them to generate the required thermal energy efficiently when an electric current passes through them.

Additionally, heating elements in appliances like electric irons operate at very high temperatures. At these elevated temperatures, pure metals tend to react with oxygen in the air (oxidise or burn) relatively easily, which can quickly damage or destroy the element. Alloys, however, do not oxidise or burn readily even at high temperatures, ensuring the durability, safety, and longevity of the heating element.