Rana Pratap Sagar Dam, an important hydroelectric and irrigation structure in Rajasthan, is built across which of the following rivers?

Introduction / Context:
India has many major dams built on important rivers for irrigation, power generation and flood control. Rana Pratap Sagar Dam is one such dam in Rajasthan, often mentioned in questions about river valley projects and state wise dams. Knowing which river it crosses helps you connect physical geography with infrastructure. This question tests your ability to associate the name of the dam with the correct river system.

Given Data / Assumptions:

- The dam mentioned is Rana Pratap Sagar Dam. - It is located in the state of Rajasthan. - The options for rivers are Ghagra, Yamuna, Kosi and Chambal. - Candidates are expected to know or recall the main river on which this dam is built.

Concept / Approach:
The Chambal river is a major tributary of the Yamuna and flows through Madhya Pradesh, Rajasthan and a part of Uttar Pradesh. In Rajasthan, several dams have been constructed on the Chambal as part of the Chambal Valley Project. Rana Pratap Sagar Dam is one of these key structures, located downstream of Gandhi Sagar Dam. To solve the question, you need to remember that Rana Pratap Sagar Dam belongs to the Chambal river system rather than to other Himalayan rivers listed in the options.

Step-by-Step Solution:

Verification / Alternative check:
You can verify this by consulting river project lists or maps of Rajasthan that show major dams and the rivers they cross. In such lists, Rana Pratap Sagar Dam is consistently placed on the Chambal river. The grouping of Gandhi Sagar, Rana Pratap Sagar and Jawahar Sagar together under the Chambal Valley Project further confirms this association. Since no reliable reference places the dam on Ghagra, Yamuna or Kosi directly, Chambal is clearly the correct river in exam contexts.

Why Other Options Are Wrong:
Ghagra (also spelled Ghaghara) flows mainly through Uttar Pradesh and Bihar and is not the site of Rana Pratap Sagar Dam. Yamuna is the parent river of the Chambal system, but the dam is specifically on the Chambal tributary, not upstream on the Yamuna itself. Kosi flows through Bihar and Nepal and is known for flooding issues, not for this particular dam. None of the above would apply only if there were no correct river listed, but Chambal is correctly listed and must be chosen.

Common Pitfalls:
Some candidates see both Yamuna and Chambal and get confused because Chambal is a tributary of Yamuna. They may incorrectly choose Yamuna thinking of the larger river, forgetting that the dam is actually constructed on the tributary itself. Others might guess randomly among the Himalayan rivers Ghagra and Kosi without relating the question to Rajasthan. To avoid such mistakes, learn a few key dam river pairs thoroughly, such as Rana Pratap Sagar Chambal and Bhakra Nangal Sutlej.

Final Answer:
Rana Pratap Sagar Dam in Rajasthan is built across the Chambal river.