Renal artery brings oxygenated blood to the kidneys from the aorta which arises out of heart but this blood is not pure and has nitrogenous waste in it while renal vein carries deoxygenated but filtered blood to the heart from where it is again pumped to the entire body.

Yes, option B is correct. You should read ncert thoroughly to get a grip on concepts.

Understanding Nitrogenous Waste in Blood Vessels
In the human circulatory system, different blood vessels have varying concentrations of nitrogenous waste. This can be understood by analyzing the functions of the renal and pulmonary circulation.
1. Renal Vein and Nitrogenous Waste
- The renal vein is responsible for transporting blood away from the kidneys.
- After the kidneys filter the blood, they remove excess nitrogenous waste (like urea) and other impurities.
- Therefore, the renal vein contains significantly less nitrogenous waste compared to other blood vessels.
2. Comparison with Other Vessels
- Pulmonary Artery: This vessel carries deoxygenated blood from the heart to the lungs. It contains metabolic waste products but is not primarily involved in nitrogenous waste removal.
- Pulmonary Vein: The pulmonary vein carries oxygenated blood from the lungs to the heart and generally contains minimal waste products, but it is still not as clean as the renal vein.
- Renal Artery: This artery supplies blood to the kidneys for filtration. The blood here has a higher concentration of nitrogenous waste before it is processed by the kidneys.
Conclusion
Given the roles of these blood vessels, the renal vein is the correct answer as it contains the least nitrogenous waste. It serves as the cleaned vessel after filtration, unlike the renal artery, pulmonary artery, and pulmonary vein, which either transport waste or have not undergone filtration yet.