**Core Concept**
Chronic laxative abuse can disrupt normal bowel habits, leading to changes in urine composition and increasing the risk of certain types of kidney stones. This is often due to the body's attempt to compensate for the loss of electrolytes and water through excessive bowel movements.

**Why the Correct Answer is Right**
Chronic laxative abuse can cause the body to retain more ammonium ions, which are then excreted in the urine. In the presence of excess ammonium ions, the urine becomes more alkaline, favoring the formation of ammonium urate stones. Ammonium urate stones are a type of uric acid stone that forms in alkaline urine, often as a result of chronic laxative abuse or other conditions that lead to ammonium ion retention. The increased ammonium ion concentration in the urine also contributes to the formation of these stones.

**Why Each Wrong Option is Incorrect**
**Option A:** Xanthine stones are rare and usually occur in patients with xanthinuria, a genetic disorder that affects the metabolism of xanthine. Chronic laxative abuse is not typically associated with this condition.
**Option B:** Cysteine stones are more commonly seen in patients with cystinuria, a genetic disorder that affects the reabsorption of cystine in the kidneys. Chronic laxative abuse is not a known risk factor for cystine stone formation.
**Option D:** Struvite stones, also known as magnesium ammonium phosphate stones, are typically associated with urinary tract infections (UTIs) caused by urease-producing bacteria. Chronic laxative abuse is not a known risk factor for struvite stone formation.

**Clinical Pearl / High-Yield Fact**
Patients with a history of chronic laxative abuse should be monitored for signs of electrolyte imbalances and changes in urine composition, as these can increase the risk of kidney stone formation.

**✓ Correct Answer: C. Ammonium urate**