Graphite is used as a dry lubricant due to the presence of

Step 1: Analyze the question The question asks why graphite can act as a dry lubricant, meaning why it feels slippery and lets surfaces slide over each other.

Step 2: Explain the concept Graphite is a giant covalent structure of carbon with these features:

• Each carbon atom is covalently bonded to three other carbon atoms in flat hexagonal rings. This forms a flat sheet, or layer.
• The fourth valence electron of each carbon is delocalised (mobile) within the layer. This is why graphite conducts electricity.
• The layers are held together only by weak van der Waals forces.

Step 3: Apply it Because the forces between the layers are weak, the layers slide over one another easily when pressure is applied. This sliding is what makes graphite slippery and useful as a dry lubricant, for example in machine parts and pencil "lead".

Step 4: Check each option

• A. Mobile electrons: These explain graphite's electrical conductivity, not its lubricating property.
• B. Free electrons: This is the same idea as A, so it also relates to conductivity.
• C. Octahedral structures: Graphite has no such structure. Its structure is planar hexagonal.
• D. Layered structures: Correct. Layers held by weak forces slide over each other.

Answer: D. Layered structures

Exam tip: Link each property of graphite to its cause:

• Conducts electricity → delocalised (mobile) electrons
• Lubricant and soft → layers with weak van der Waals forces
• Diamond is hard → a rigid 3D network of covalent bonds