**Core Concept**
Acidification of urine is a physiological process that occurs in the kidneys, where the pH of the urine is decreased to eliminate excess hydrogen ions (H+) and maintain acid-base balance in the body. This process is crucial for the elimination of acidic substances, such as uric acid and other organic acids, from the body.

**Why the Correct Answer is Right**
The kidneys achieve acidification of urine by increasing the secretion of hydrogen ions (H+) into the distal convoluted tubule and collecting ducts. This is mediated by the enzyme carbonic anhydrase and the Na+/H+ exchanger in the renal tubular cells. The increased secretion of hydrogen ions decreases the pH of the urine, allowing for the elimination of acidic substances. Additionally, the kidneys reabsorb bicarbonate ions (HCO3-) from the filtrate, which helps to further acidify the urine.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the process of acidification of urine. While the kidneys do regulate the pH of the urine, they do not achieve this by increasing the pH.
* **Option B:** This option is incorrect because it is actually the opposite of what occurs in acidification of urine. The kidneys do not increase the pH of the urine by increasing the reabsorption of bicarbonate ions.
* **Option C:** This option is incorrect because it is a partial mechanism, but not the primary mechanism, of acidification of urine. While the kidneys do regulate the pH of the urine, the primary mechanism is the secretion of hydrogen ions into the distal convoluted tubule and collecting ducts.

**Clinical Pearl / High-Yield Fact**
In patients with kidney disease or acid-base disorders, the kidneys may have impaired ability to acidify the urine, leading to metabolic acidosis. This is a critical clinical scenario that requires prompt recognition and management to prevent complications.

**Correct Answer:** D.