Graphite cannot be used as a lubricant in space because

Options

A. absence of external pressure tranforms crystalline graphite to amorphous form .
B. there is no atmosphere in sapce and hence graphite sublimes in space.
C. there is no atmosphere in space and hence there is no adsorbed air and water between layers of graphite.
D. None of the above.

Answer

**Step-by-Step Solution:**

1. **Understanding Graphite as a Lubricant:**
- Graphite is commonly used as a lubricant due to its layered structure. The layers of graphite can slide over each other easily because they are held together by weak van der Waals forces.

2. **Conditions in Space:**
- In space, there is no atmosphere, which means there is a lack of air and water. These elements are crucial for maintaining the slippery nature of graphite.

3. **Effect of Absence of Atmosphere:**
- The absence of air and water means that there are no adsorbed molecules between the layers of graphite. Without these adsorbed substances, the layers cannot slide over each other effectively.

4. **Analyzing the Options:**
- **Option 1:** Absence of external pressure transforms crystalline graphite to amorphous form. (Incorrect)
- **Option 2:** There is no atmosphere in space and hence graphite sublimes in space. (Incorrect)
- **Option 3:** There is no atmosphere in space and hence, there is no adsorbed air and water between the layers of graphite. (Correct)
- **Option 4:** None of these. (Incorrect)

5. **Conclusion:**
- The correct answer is **Option 3**: Graphite cannot be used as a lubricant in space because there is no atmosphere, and therefore, there is no adsorbed air and water between the layers of graphite.

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