Assertion: The time of vulcanisation and temperature is increased by adding accelerators.
Reason: By vulcanising, a material of high tensile strength can be obtained

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the corret explanation of the assertion.
C. if assertion is true but reason is false
D. if the assertion and reason both are false

Explanation

To solve the question, we will analyze the assertion and the reason provided, and determine their validity.

### Step-by-step Solution:

1. **Understanding the Assertion**:
- The assertion states that "The time of vulcanisation and temperature is increased by adding accelerators."
- In vulcanization, accelerators are substances that speed up the chemical reaction between rubber and sulfur, which helps in forming cross-links.
- **Conclusion**: This statement is false because adding accelerators actually decreases the time of vulcanization, not increases it.

2. **Understanding the Reason**:
- The reason states that "By vulcanising, a material of high tensile strength can be obtained."
- Vulcanization does indeed lead to the formation of a material with high tensile strength due to the cross-linking of sulfur in the rubber.
- **Conclusion**: This statement is true. Vulcanization increases the tensile strength of rubber.

3. **Evaluating the Relationship**:
- The assertion is false, while the reason is true.
- In logical terms, the reason does not support the assertion because the assertion is incorrect.

4. **Final Conclusion**:
- Since the assertion is false and the reason is true, the correct answer is that both statements are not true together.

### Answer:
Both the assertion and the reason are not true together. The assertion is false, and the reason is true.