Name the substance which is used in lubrication :

Options

A. Lubricating oil
B. Lubricating fibre
C. Both of the above
D. None of the above

Explanation

**Step-by-Step Solution:**

1. **Understanding Lubrication**: Lubrication is the process of reducing friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move.

2. **Identifying Lubricating Substances**: There are various substances used for lubrication, but the most common and widely recognized one is lubricating oil.

3. **Function of Lubricating Oil**: Lubricating oil creates a thin film or layer on the surfaces of metal components. This oil film transforms solid friction into liquid friction, which is much less, thereby reducing wear and tear on the mechanical parts.

4. **Importance of Reducing Friction**: In machines, when two surfaces are in motion, friction is generated. High friction can lead to overheating and damage to the components. Therefore, lubricating oil is essential to ensure smooth operation.

5. **Conclusion**: The substance that is primarily used for lubrication is lubricating oil.

**Final Answer**: The substance which is used in lubrication is lubricating oil.

---