📘 IAS Prelims 2025 — GS-I Q.23 | Classroom Explanation

📌 Question

Q.23) Consider the following water bodies:

I. Lake Tanganyika
II. Lake Tonlé Sap
III. Patos Lagoon

Through how many of them does the Equator pass?

(a) Only one
(b) Only two
(c) All the three
(d) None

✅ Correct Answer: (d)

🧑‍🏫 Classroom Explanation

This question tests latitudinal awareness combined with world geography, a classic UPSC elimination area involving Equator, Tropics, and major water bodies.

🔍 Key Concept: Equator (0° Latitude)

• The Equator (0°) divides Earth into Northern and Southern Hemispheres
• Passes through:

• South America
• Africa
• Southeast Asia (Indonesia region)
• Major oceans (Atlantic, Pacific, Indian)

UPSC often frames trap questions where a feature lies near the equator but not on it.

🔍 Water Body–wise Analysis

❌ Lake Tanganyika

• Located in East Africa
• Extends roughly between 3°S to 9°S latitude
• Lies entirely south of the Equator
• Part of the Western Rift Valley of the East African Rift System

Extra info:

• Longest freshwater lake in the world (≈660 km)
• Second deepest lake after Lake Baikal
• Borders Tanzania, DRC, Burundi, Zambia

➡️ Equator does NOT pass through Lake Tanganyika

❌ Lake Tonlé Sap

• Located in central Cambodia
• Lies around 13°N latitude
• Connected to the Mekong River via the Tonlé Sap River

Extra info:

• Famous for seasonal flow reversal
• Expands up to 5 times during monsoon
• UNESCO Biosphere Reserve

➡️ Far north of the Equator

❌ Patos Lagoon

• Located in southern Brazil
• Lies around 30°S latitude
• Situated well within the Southern Hemisphere

Extra info:

• Largest lagoon in Brazil
• Second largest lagoon in South America
• Separated from Atlantic Ocean by sand barriers

➡️ Far south of the Equator

🧮 Logical Elimination (UPSC Style)

• Lake Tanganyika → South of Equator
• Lake Tonlé Sap → North of Equator
• Patos Lagoon → Far South of Equator

➡️ Equator passes through none of the given water bodies

🎯 Final Answer

✅ Correct Answer: (d) None

🔗 Extra Info Points (Prelims Gold)

• Equator passes through:

• Lake Victoria (Africa)
• Amazon Basin (South America)
• Indonesia (island chains)

• UPSC often confuses:

• Lake Tanganyika ❌ (south of Equator)
• Lake Victoria ✅ (crossed by Equator)

🗺️ Map-Based Visual Reinforcement

📍 GS Mapping

GS Paper I
Subject: Geography
Theme: Latitude, Physical Geography
Nature: Conceptual + Map-based Elimination

🧠 Final Memory Lock

Equator loves rivers and basins, not long rift lakes.