To determine the INCORRECT statement among the provided options, let's analyze each statement step by step.
### Step 1: Analyze Statement (a)
**Statement (a)**: "During urine formation, the tubular cells secrete substances like `H^+, Na^+, and HCO_3^-` into the filtrate."
- **Explanation**: Tubular secretion is a process where certain substances are secreted into the renal tubules from the blood. Common substances secreted include H+ ions and K+ ions, which help in maintaining acid-base balance. However, Na+ and HCO3- are primarily reabsorbed rather than secreted. Therefore, this statement is **incorrect**.
### Step 2: Analyze Statement (b)
**Statement (b)**: "As glomerular filtrate moves down in the descending limb of Henle, it gets concentrated and as concentrated filtrate passes upward in ascending limb of HL, it gets diluted."
- **Explanation**: The descending limb of the loop of Henle is permeable to water but not to solutes, leading to water reabsorption and concentration of the filtrate. Conversely, the ascending limb is impermeable to water but allows solute reabsorption, leading to dilution of the filtrate. This statement is **correct**.
### Step 3: Analyze Statement (c)
**Statement (c)**: "Conditional reabsorption of `Na^+` and water takes place in PCT."
- **Explanation**: The proximal convoluted tubule (PCT) does reabsorb a significant amount of Na+ and water, but the term "conditional" may imply that it doesn't occur consistently. However, the PCT is primarily responsible for the reabsorption of these substances. Thus, this statement can be considered **correct**.
### Step 4: Analyze Statement (d)
**Statement (d)**: "Reabsorption in ascending limb of HL is minimum."
- **Explanation**: The ascending limb of the loop of Henle does have a lower reabsorption capacity compared to the PCT, but it is not accurate to say that reabsorption is minimum overall; it is significant for certain ions. However, compared to the PCT, it is indeed lower. Therefore, this statement is **correct**.
### Conclusion
After analyzing all statements:
- **Incorrect Statements**: (a) and (c)
- **Correct Statements**: (b) and (d)
Thus, the INCORRECT statements are **(a)** and **(c)**.
### Final Answer
The INCORRECT statement is **(a)**.
