To determine which statement is true regarding lenses, we will analyze the given options based on the principles of optics, specifically focusing on the power and focal length of convex and concave lenses.
### Step-by-Step Solution:
1. **Understanding Lens Power and Focal Length**:
- The power (P) of a lens is given by the formula:
\[
P = \frac{1}{f}
\]
where \(f\) is the focal length in meters.
- For a convex lens, the focal length is positive, and thus the power is also positive.
- For a concave lens, the focal length is negative, leading to a negative power.
2. **Analyzing Option A**:
- Option A states: "A convex lens has 4D power having focal length of 0.25 meter."
- Since the power is positive (4D) and the focal length is also positive (0.25 m), this statement is consistent with the properties of a convex lens.
- Therefore, Option A is **correct**.
3. **Analyzing Option B**:
- Option B states: "The convex lens has -4D power, having aperture equal to 0.25."
- Here, the power is negative, which contradicts the nature of a convex lens (which should have positive power).
- Hence, Option B is **incorrect**.
4. **Analyzing Option C**:
- Option C states: "The concave lens has 4D power, having aperture equal to 0.25 meter."
- A concave lens should have negative power since its focal length is negative. Thus, having a positive power (4D) is incorrect.
- Therefore, Option C is **incorrect**.
5. **Analyzing Option D**:
- Option D states: "The concave lens has -4D power and aperture equal to 0.25 meter."
- While the power is correctly negative for a concave lens, the focal length must also be negative. The statement does not specify the focal length but implies it could be positive, which is incorrect.
- Hence, Option D is **incorrect**.
### Conclusion:
Based on the analysis, the only true statement is **Option A**: "A convex lens has 4D power having focal length of 0.25 meter."
