Which of the following does not describe a physical property of iron?
A Iron is silvery-white or gray in color.
B Iron has a boiling point of about 3,000°C.
C Iron is a magnetic element.
D Iron and sulfur react to form iron sulfide.
The Correct Answer and Explanation is :
The correct answer is D. Iron and sulfur react to form iron sulfide.
This statement describes a chemical property of iron, not a physical one. To understand why, let’s break down the distinction between physical and chemical properties.
Physical Properties
A physical property of a substance is one that can be observed or measured without changing the substance’s chemical identity. Some of the common physical properties of materials include:
- Color: For iron, this is typically silvery-white or gray (as mentioned in Option A).
- Boiling point and melting point: Iron has a high boiling point, approximately 3,000°C (as stated in Option B), and a melting point of around 1,538°C. These are physical properties because they describe the state changes of iron without altering its chemical composition.
- Magnetism: Iron is a magnetic element (as noted in Option C), meaning it can be attracted to magnets or be magnetized. This is a physical trait because it relates to iron’s behavior in a magnetic field without changing its structure.
Chemical Properties
In contrast, a chemical property describes a substance’s ability to undergo a chemical reaction and form new substances. These properties are only observed when a chemical change occurs.
In Option D, the reaction of iron with sulfur to form iron sulfide is an example of a chemical change. When iron reacts with sulfur, a new compound (iron sulfide, FeS) is formed, which has different properties from the original elements. This transformation indicates a change in the chemical identity of iron, which makes it a chemical property rather than a physical one.
Therefore, Option D does not describe a physical property of iron.