An allotrope is a different form or arrangement of atoms of an element in the same physical state. Oxygen, sulphur, and carbon all have allotropes, but nitrogen does not.

Option 1: Oxygen has two common allotropes - oxygen gas (O2) and ozone (O3). Oxygen gas is the most stable form of oxygen found in the Earth`s atmosphere.

Option 2: Sulphur has several allotropes, including the most common forms - rhombic sulphur (S8) and monoclinic sulphur. These allotropes differ in their molecular structures and physical properties.

Option 3: Nitrogen does not have any known stable allotropes. Nitrogen exists predominantly as a diatomic molecule (N2) in its most stable form.

Option 4: Carbon is well-known for its allotropes. Some of the most common carbon allotropes include diamond, graphite, and fullerenes. Each of these allotropes has a distinct arrangement of carbon atoms, giving them different properties.

In summary, nitrogen is the correct answer as it does not have any known stable allotropes.