**Core Concept**
The question is testing the knowledge of the appropriate infusion time for dialysate in patients undergoing hemodialysis, specifically in the context of chronic renal failure. This requires understanding the principles of renal replacement therapy and the importance of optimizing dialysis parameters to achieve effective toxin removal.

**Why the Correct Answer is Right**
In patients with chronic renal failure, the dialysis process involves the exchange of solutes between the blood and the dialysate. The infusion time for the dialysate is critical in ensuring that the desired level of solute removal is achieved. A shorter infusion time, such as 15 minutes, allows for a more efficient exchange of solutes, which is essential for patients with severe renal impairment. This is because the dialysate needs to be changed frequently to maintain a high concentration gradient for solute removal.

**Why Each Wrong Option is Incorrect**
**Option B:** 30 minutes is too long, as it may lead to a decrease in the concentration gradient for solute removal, reducing the effectiveness of the dialysis process.

**Option C:** 1 hour is excessively long and may result in inadequate solute removal, leading to a buildup of toxins in the blood.

**Option D:** 2 to 3 hours is not only impractical but also ineffective, as it would significantly compromise the dialysis process and potentially lead to severe electrolyte imbalances and fluid overload.

**Clinical Pearl / High-Yield Fact**
In patients undergoing hemodialysis, it is essential to maintain a high dialysate flow rate and a short infusion time to ensure effective solute removal and prevent the buildup of toxins in the blood.

**✓ Correct Answer: A. 15 minutes**