Geography · Ocean Currents of the World
The concept being tested: Equatorial location of major lakes and lagoons.
Consider the following water bodies: I. Lake Tanganyika II. Lake Tonlé Sap III. Patos Lagoon Through how many of them does the equator pass?
The equator is a fixed line at zero degrees latitude, and none of these three water bodies lie on it. Lake Tanganyika, part of the East African Rift Valley, stretches roughly between 3 degrees and 9 degrees south latitude, placing it entirely in the Southern Hemisphere well clear of the equator; it is often confused with Lake Victoria, which the equator does cross. Lake Tonle Sap in Cambodia sits near 13 degrees north latitude, deep in mainland Southeast Asia, far north of the line. Patos Lagoon, South America's largest lagoon, runs along the southern Brazilian coast between about 30 and 32 degrees south latitude, closer to the Tropic of Capricorn than to the equator. Since not one of the three touches zero degrees latitude, the option stating that the equator passes through none of them is correct.
What UPSC was testing
UPSC is testing precise latitude recall rather than a loose sense that African rift lakes are equatorial; the trap is confusing Lake Tanganyika with the neighbouring Lake Victoria, the actual equator-crossing Great Lake, while the only-two-all-none framing punishes anyone answering from vague geographic memory.
How often this comes up
This concept has appeared 8 times in UPSC Prelims General Studies Paper I between 2015 and 2025 — in 2015, 2017, 2018, 2021, 2024 and 2025.
The option-by-option autopsy for this question — why each of the other three is wrong, and which neighbouring concept each one was built from — is in the app.