Answer the question by choosing responses from the following:  
1) Sodium: plays a crucial role in the reabsorption of H+ ions in the kidneys.
2) Potassium: Present outside the cell in 10 times higher concentration than inside. 
3) Calcium: Its concentration in the blood is increased by parathyroid hormone (PTH). 
4) Hydrogen ions: are secreted in the renal tubules to reabsorb K+ ions. 
5) Phosphate: Parathyroid hormone (PTH) acts on the kidneys to decrease phosphate reabsorption, resulting in increased urinary excretion of phosphate. 
6) Ammonium ions: helps in the formation of urea in the DCT.   


Which of the above options correctly matches the ions with their description?

• A. 1 and 2.
• B. 2, 3, and 6.
• C. 3 and 5.
• D. 4, 5, and 6.

Answer: (C)