The arrows in NCERT Book are inverse so don't be confuse option C is right.

PCT (Proximal Convoluted Tubule) plays a crucial role in maintaining the pH and ionic balance of body fluids. It accomplishes this through the processes of selective secretion and reabsorption.

Selective Secretion:
PCT selectively secretes certain ions in the filtrate, such as H+ (hydrogen ions), NH3 (ammonia), and K+ (potassium ions).

- H+ ions: The secretion of hydrogen ions helps regulate the pH of body fluids. If the blood becomes too acidic, the PCT can secrete excess hydrogen ions into the filtrate, thus reducing the acidity. On the other hand, if the blood becomes too alkaline, the PCT can decrease the secretion of hydrogen ions, helping to maintain a balanced pH.

- NH3 ions: Ammonia is produced as a waste product during amino acid metabolism. PCT secretes NH3 ions into the filtrate, which combines with hydrogen ions to form NH4+ (ammonium ions). This process helps eliminate excess ammonia from the body, preventing the accumulation of toxic levels.

- K+ ions: The PCT also secretes potassium ions into the filtrate. This secretion helps maintain the balance of potassium levels in the body fluids. It is crucial for various physiological processes, including nerve and muscle function.

Reabsorption of HCO-3:
PCT also plays a role in reabsorbing HCO-3 (bicarbonate ions) from the filtrate. Bicarbonate ions are essential in maintaining the acid-base balance in the body. They act as a buffer, helping to regulate the pH by neutralizing excess acids or bases. By reabsorbing bicarbonate ions, the PCT helps to maintain the appropriate levels of this important buffer in the body.

The Combined Effect:
The selective secretion of H+, NH3, and K+ ions, along with the reabsorption of bicarbonate ions, collectively contribute to the maintenance of pH and ionic balance in body fluids. These processes ensure that the body's internal environment remains within the optimal range for normal physiological functions.

In addition, the PCT does not secrete regulatory hormones like renin and angiotensinogen. These hormones are primarily secreted by the juxtaglomerular apparatus, which is located in the kidney's nephrons. They play a role in regulating blood pressure and fluid balance, but are not directly involved in maintaining the pH and ionic balance of body fluids, as stated in option 'd'. Therefore, the correct answer is option 'c', which includes selective secretion and bicarbonate reabsorption by the PCT.