**Core Concept**
Rickets is a disorder of bone development in children, characterized by softening of the bones due to defective mineralization. The condition is primarily caused by disturbances in calcium and phosphate metabolism, which are essential for bone mineralization.

**Why the Correct Answer is Right**
The correct answer involves the loss of phosphate in urine (D) and decreased absorption of calcium (c). Phosphate is an essential component of hydroxyapatite, the mineral form of calcium found in bones. A deficiency in phosphate leads to impaired bone mineralization, resulting in rickets. Similarly, decreased absorption of calcium from the gut further exacerbates the condition by reducing the available calcium for bone mineralization.

**Why Each Wrong Option is Incorrect**
* **Option A:** Loss of calcium in urine (a) is not a primary cause of rickets. While excessive loss of calcium can contribute to the condition, it is not the underlying mechanism.
* **Option B:** Increased mobilization of calcium from bone (b) is actually a compensatory response to decreased calcium absorption, rather than a cause of rickets.
* **Option C:** The combination of increased mobilization of calcium from bone (b) and loss of phosphate in urine (d) is incorrect because increased mobilization of calcium from bone is a response to decreased calcium absorption, not a cause of rickets.

**Clinical Pearl / High-Yield Fact**
Rickets can be prevented with adequate intake of calcium and vitamin D, which enhances calcium absorption from the gut. Vitamin D deficiency is a common cause of rickets in children, particularly in regions with limited sunlight.

✓ Correct Answer: D. cd. Loss of phosphate in urine and decreased absorption of calcium.