The counter current system of vasa rectae retains the reabsorbed `Na^(+)` in the medullary tissue.

Answer

### Step-by-Step Solution:

1. **Understanding the Structure**: The vasa recta are specialized blood vessels that run parallel to the loop of Henle in the nephron of the kidney. They play a crucial role in the kidney's ability to concentrate urine.

2. **Countercurrent Mechanism**: The countercurrent mechanism refers to the flow of filtrate in the loop of Henle and the flow of blood in the vasa recta occurring in opposite directions. This arrangement helps maintain a concentration gradient in the medullary interstitium.

3. **Role of NaCl and Urea**: The concentration gradient in the medulla is primarily maintained by sodium chloride (NaCl) and urea. As the filtrate moves through the ascending limb of the loop of Henle, NaCl is actively transported out into the interstitium.

4. **Reabsorption Process**: The descending limb of the vasa recta allows for the passive reabsorption of NaCl from the interstitium, while the ascending limb of the vasa recta returns NaCl back to the bloodstream. This process ensures that NaCl remains concentrated in the medullary tissue.

5. **Conclusion**: The statement that "the counter current system of vasa rectae retains the reabsorbed Na^(+) in the medullary tissue" is true. The vasa recta effectively retain Na^+ in the medullary tissue through the countercurrent exchange mechanism.