(A) : In electromagnetic waves electric field and magnetic field lines are perpendicular to each other. (R) : Electric field and magnetic field are self sustaining.

Options

A. Both 'A' and 'R' are true and 'R' is the correct explanation of 'A'.
B. Both 'A' and ’R' are true and 'R' is not the correct explanation of 'A
C. A' is true and 'R' is false
D. 'A' is false and R' is true

Answer

To solve the question, we need to analyze the assertion (A) and the reason (R) provided.

### Step 1: Analyze the Assertion (A)
The assertion states that "In electromagnetic waves, electric field and magnetic field lines are perpendicular to each other."

- In electromagnetic waves, the electric field (E) and magnetic field (B) are indeed perpendicular to each other. This is a fundamental property of electromagnetic waves. Additionally, they are also perpendicular to the direction of wave propagation.

### Step 2: Analyze the Reason (R)
The reason states that "Electric field and magnetic field are self-sustaining."

- This statement is also true. In electromagnetic waves, the electric field generates a magnetic field, and the changing magnetic field generates an electric field. This mutual generation allows the wave to propagate through space without the need for a medium, making them self-sustaining.

### Step 3: Determine the Relationship Between A and R
Now we need to determine if the reason (R) correctly explains the assertion (A).

- While both statements are true, the reason does not directly explain why the electric and magnetic fields are perpendicular to each other. The perpendicular nature of E and B is a result of Maxwell's equations and the wave nature of electromagnetic radiation, not merely because they are self-sustaining.

### Conclusion
Based on the analysis:
- Assertion (A) is true.
- Reason (R) is true.
- However, R does not correctly explain A.

Thus, the correct answer is: Both A and R are true, but R is not the correct explanation of A.