Assertion: Phosphorus cycle is an imperfect cycle as a sufficient amount of phosphorus combines with `Al^(3+) Fe^(2+)` and `Ca^(2+)` to form insoluble and unavailable salts.
Reason: Phosphate circulation in abiotic environment in lithosphere as well as in atmosphere.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion:**
- The assertion states that the phosphorus cycle is an imperfect cycle because a significant amount of phosphorus combines with aluminum (Al³⁺), iron (Fe²⁺), and calcium (Ca²⁺) to form insoluble and unavailable salts. This means that not all phosphorus is readily available for biological uptake, which is a characteristic of an imperfect cycle.

2. **Understanding the Reason:**
- The reason provided claims that phosphate circulates in the abiotic environment, specifically in the lithosphere (earth's crust) and atmosphere. However, it is important to note that the phosphorus cycle does not involve a gaseous phase, which is a key characteristic of a perfect cycle.

3. **Evaluating the Assertion:**
- The assertion is correct. The phosphorus cycle is indeed considered imperfect due to the formation of insoluble phosphates that are not available for biological use. This leads to a limitation in the availability of phosphorus in ecosystems.

4. **Evaluating the Reason:**
- The reason is incorrect. While phosphate does circulate in the lithosphere (soil and rocks) and hydrosphere (water bodies), it does not circulate in the atmosphere as a gas, which is a defining feature of a complete cycle. Therefore, the statement about the atmosphere is false.

5. **Conclusion:**
- Since the assertion is true and the reason is false, the correct relationship is that the assertion is correct, but the reason is not a correct explanation of the assertion.

**Final Answer:**
- The assertion is true, and the reason is false.

---