A : In an electromagnetic wave the energy density in electric field is equal to energy density in magnetic field.
R : Electromagnetic waves are transverse in nature.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

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

### Step-by-Step Solution:

1. **Understanding Assertion (A)**:
- The assertion states that in an electromagnetic (EM) wave, the energy density in the electric field is equal to the energy density in the magnetic field.
- The energy density \( u_E \) in the electric field is given by the formula:
\[ u_E = \frac{1}{2} \epsilon_0 E^2 \]
- The energy density \( u_B \) in the magnetic field is given by the formula:
\[ u_B = \frac{1}{2} \frac{B^2}{\mu_0} \]
- In an EM wave, the relationship between the electric field \( E \) and the magnetic field \( B \) is given by:
\[ E = cB \]
where \( c \) is the speed of light.
- Substituting \( B = \frac{E}{c} \) into the equation for \( u_B \):
\[ u_B = \frac{1}{2} \frac{(E/c)^2}{\mu_0} = \frac{1}{2} \frac{E^2}{c^2 \mu_0} \]
- Since \( c = \frac{1}{\sqrt{\epsilon_0 \mu_0}} \), we can show that:
\[ u_E = u_B \]
- Therefore, the assertion (A) is correct.

2. **Understanding Reason (R)**:
- The reason states that electromagnetic waves are transverse in nature.
- A transverse wave is characterized by oscillations that are perpendicular to the direction of wave propagation.
- In the case of EM waves, the electric field and magnetic field oscillate perpendicular to each other and to the direction of propagation, confirming that EM waves are indeed transverse.

3. **Relationship between Assertion and Reason**:
- While both the assertion and the reason are correct, the reason does not directly explain the assertion. The equality of energy densities in electric and magnetic fields is a result of their intrinsic properties in an EM wave, while the transverse nature of EM waves is a separate characteristic.

4. **Conclusion**:
- Both the assertion (A) and reason (R) are correct, but the reason does not explain the assertion. Therefore, the correct option is that both statements are true, but the reason is not the correct explanation for the assertion.

### Final Answer:
- Assertion (A) is true.
- Reason (R) is true, but it does not explain (A).