Sulphur exists in six forms in the solid state. This property is known as

Analysis

The question asks for the specific term used to describe the ability of an element, like sulphur, to exist in more than one physical form in the same state (solid).

Concept Explanation

• Allotropy: This is the property whereby an element can exist in two or more different physical forms in the same physical state. These forms are called allotropes. Common examples include carbon (diamond and graphite) and sulphur (rhombic and monoclinic sulphur).
• Isomerism: This refers to compounds that have the same molecular formula but different structural arrangements. This is common in organic chemistry (e.g., butane and isobutane).
• Isotopy: This refers to atoms of the same element that have the same atomic number but different mass numbers (different number of neutrons).
• Isomorphism: This is the phenomenon where two or more different substances crystallize in the same geometric form (e.g., potash alum and chrome alum).

Step-by-Step Solution

1. Identify the subject: The question focuses on "Sulphur" and its "six forms in the solid state."
2. Evaluate the definitions: Since sulphur is a single element and the question describes different physical forms of that same element, we are looking for the definition of allotropy.
3. Compare with options: • Isomerism applies to molecules/compounds. • Isotopy applies to atoms of the same element. • Isomorphism applies to different substances with the same crystal shape. • Allotropy is the only term that describes different forms of the same element.

Conclusion

The property of an element existing in different forms in the same physical state is known as Allotropy.

Exam Tip: To remember this easily, think of the "A" in Allotropy as standing for Another form of the same element. Don't confuse it with Isotopes, which are about the nucleus (protons/neutrons), whereas Allotropes are about the physical arrangement of the atoms.