In the following question a statement of assertion (A) is followed by a statement of reason (R )
A: If E be electric field at a point , in free space then energy density at that point will be `(1)/(2) epsilon_(0)E^(2)` .
R , electrostatic field is a conservative field .

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 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 the assertion (A) and the reason (R) given in the problem.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that if \( E \) is the electric field at a point in free space, then the energy density at that point will be given by the formula:
\[ u = \frac{1}{2} \epsilon_0 E^2 \]
- Here, \( \epsilon_0 \) is the permittivity of free space, and \( E \) is the magnitude of the electric field.

2. **Understanding the Reason (R)**:
- The reason states that the electrostatic field is a conservative field.
- A conservative field is one where the work done in moving a charge between two points is independent of the path taken. In electrostatics, this means that the electric potential energy depends only on the initial and final positions of the charge.

3. **Evaluating the Assertion**:
- The formula for energy density \( u = \frac{1}{2} \epsilon_0 E^2 \) is indeed correct for an electric field in free space. This represents the energy stored per unit volume in the electric field.

4. **Evaluating the Reason**:
- The electrostatic field is indeed a conservative field. This is a fundamental property of electrostatic fields, which allows us to define electric potential.

5. **Conclusion**:
- Both the assertion (A) and the reason (R) are correct. However, the reason does not directly explain the assertion. The energy density formula is a general property of electric fields, and while it is true that electrostatic fields are conservative, the assertion about energy density does not rely on this fact.

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