निम्नलिखित कथनों पर विचार कीजिए : कथन I. जनवरी में, उत्तरी गोलार्ध में, समताप रेखाएँ भूखण्डों से गुजरती हुई विषुवत् वृत्त की ओर मुड़ती हैं, जबकि महासागरों से गुजरती हुई ध्रुवों की ओर मुड़ती हैं। कथन II. जनवरी में, महासागरों के ऊपर की हवा, उत्तरी गोलार्ध के भूखण्डों के ऊपर की हवा से अधिक गर्म होती है। उपर्युक्त कथनों के संदर्भ में, निम्नलिखित में से कौन-सा एक सही है?

(b) कथन I और कथन II दोनों सही हैं किन्तु कथन II, कथन I की व्याख्या नहीं करता है

(c) कथन I सही है किन्तु कथन II सही नहीं है

(d) कथन I सही नहीं है किन्तु कथन II सही है

पृथ्वी ग्रह के संदर्भ में, निम्नलिखित कथनों पर विचार कीजिए : I. वर्षा वन, महासागरों द्वारा उत्पादित ऑक्सीजन की तुलना में अधिक ऑक्सीजन उत्पादित करते हैं। II. समुद्री पादप-प्लवक और प्रकाश-संश्लेषी जीवाणु विश्व में ऑक्सीजन का लगभग 50% उत्पादित करते हैं। III. वायुमंडलीय हवा में विद्यमान ऑक्सीजन की तुलना में, सुचारू रूप से ऑक्सीकृत पृष्ठ-जल में अनेक गुना अधिक ऑक्सीजन होती है। उपर्युक्त कथनों में से कौन-सा/कौन-से सही है/हैं?

(d) उपर्युक्त कथनों में से कोई भी सही नहीं है

प्रश्न यूपीएससी के हिंदी प्रश्नपत्र से · व्याख्या अभी अंग्रेज़ी में

English हिंदी

Geography

Prelims · Geography · 16 questions

Oceans

Every UPSC Prelims question on this topic, 2016–2026, newest first. Tap an option to check yourself; the answer and explanation open below it.

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UPSC syllabus: “Indian and World Geography-Physical, Social, Economic Geography of India and the World.” Sub-topics in the detailed syllabus →

Prelims 2025 · Q27

Medium

निम्नलिखित कथनों पर विचार कीजिए :

कथन I: जनवरी में, उत्तरी गोलार्ध में, समताप रेखाएँ भूखण्डों से गुजरती हुई विषुवत् वृत्त की ओर मुड़ती हैं, जबकि महासागरों से गुजरती हुई ध्रुवों की ओर मुड़ती हैं।
कथन II: जनवरी में, महासागरों के ऊपर की हवा, उत्तरी गोलार्ध के भूखण्डों के ऊपर की हवा से अधिक गर्म होती है।

उपर्युक्त कथनों के संदर्भ में, निम्नलिखित में से कौन-सा एक सही है?

Read this question in English

Consider the following statements:

Statement-I. In January, in the Northern Hemisphere, the isotherms bend equatorward while crossing the landmasses, and poleward while crossing the oceans.

Statement-II. In January, the air over the oceans is warmer than that over the landmasses in the Northern Hemisphere.

Which one of the following is correct in respect of the above statements?

(a) Both Statement I and Statement II are correct and Statement II explains Statement I · (b) Both Statement I and Statement II are correct but Statement II does not explain Statement I · (c) Statement I is correct but Statement II is not correct · (d) Statement I is not correct but Statement II is correct

उत्तर और व्याख्या · explanation in English

Answer: (a) कथन I और कथन II दोनों सही हैं तथा कथन II, कथन I की व्याख्या करता है

In the northern winter, land loses heat fast while the oceans, helped by warm currents such as the Gulf Stream and North Atlantic Drift, stay relatively warm. A given temperature is therefore found farther north over the sea and farther south over land, so the isotherms bend poleward over oceans and equatorward over continents; the warmer ocean air is the reason.

✓ Statement-I January isotherms swing north over the North Atlantic and south over Europe and especially the Siberian plain.
✓ Statement-II Oceans cool slowly and warm currents add heat, so in January the air over them is warmer than over the cold northern landmasses; this contrast is what bends the isotherms, so II explains I.

Remember · January (NH winter): isotherms bend poleward over oceans, equatorward over land; July reverses it. Deviation is sharper in the Northern Hemisphere because it has more land.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 8 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 8 (practise this chapter)

Sources

NCERT Class 11 · Fundamentals of Physical Geography, Chapter 8 “In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean.”
NCERT Class 11 · Fundamentals of Physical Geography, Chapter 8 “The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north. Over the land the temperature decreases sharply and the isotherms bend towards south in Europe.”

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2025 · Q40

X-Ray · Core #41 Medium

पृथ्वी ग्रह के संदर्भ में, निम्नलिखित कथनों पर विचार कीजिए :

I.वर्षा वन, महासागरों द्वारा उत्पादित ऑक्सीजन की तुलना में अधिक ऑक्सीजन उत्पादित करते हैं।
II.समुद्री पादप-प्लवक और प्रकाश-संश्लेषी जीवाणु विश्व में ऑक्सीजन का लगभग 50% उत्पादित करते हैं।
III.वायुमंडलीय हवा में विद्यमान ऑक्सीजन की तुलना में, सुचारू रूप से ऑक्सीकृत पृष्ठ-जल में अनेक गुना अधिक ऑक्सीजन होती है।

उपर्युक्त कथनों में से कौन-सा/कौन-से सही है/हैं?

Read this question in English

With reference to the planet Earth, consider the following statements:

I. Rain forests produce more oxygen than that produced by oceans.

II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world’s oxygen.

III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air.

Which of the statements given above is/are correct?

(a) I and II · (b) II only · (c) I and III · (d) None of the above statements is correct

उत्तर और व्याख्या · explanation in English

Answer: (b) केवल II

The oceans, through photosynthesis by plankton and some bacteria, generate about half or more of the oxygen on Earth, so rain forests do not out-produce them: NOAA notes that one marine bacterium alone makes more oxygen than all tropical rainforests combined. Water can hold only a small amount of dissolved oxygen compared with air, so surface water never has several times more oxygen than the atmosphere.

✗ I Roughly half of Earth's oxygen production comes from the ocean (IUCN says more than half), and NOAA notes that the marine bacterium Prochlorococcus alone produces up to 20% of the biosphere's oxygen, a higher share than all the tropical rainforests combined.
✓ II NOAA says roughly half of the oxygen production on Earth comes from the ocean, mostly from oceanic plankton: drifting plants, algae and some bacteria that can photosynthesize.
✗ III NCERT notes that the amount of dissolved oxygen is fairly low compared with the amount of oxygen in air, which is why aquatic organisms breathe much faster than land ones. Water is therefore poorer in oxygen than air, not richer.

Remember · The ocean makes about half or more of Earth's oxygen (mostly phytoplankton); water holds far less oxygen than air.

📘 Read it in NCERT: Class 10 Science, Ch 5 (practise this chapter)

Sources

IUCN (with IOC-UNESCO): Ocean deoxygenation: Everyone's problem (foreword) ↗ “The ocean generates more than half the oxygen we breathe.”
NCERT Class 10 · Science, Chapter 5 “Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.”
NOAA National Ocean Service: How much oxygen comes from the ocean? ↗ “Scientists estimate that roughly half of the oxygen production on Earth comes from the ocean. The majority of this production is from oceanic plankton — drifting plants, algae, and some bacteria that can photosynthesize. … this little bacteria produces up to 20% of the oxygen in our entire biosphere . That’s a higher percentage than all of the tropical rainforests on land combined.”

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink ·

The Syllabus X-Ray of this topic

2 of its 6 sub-topics are High

0 Core · 2 High · 2 Steady · 2 Rare

HighOcean temperature, currents & salinity · 3 questions
HighLaw of the sea & deep-sea exploration · 3 questions

The X-Ray ranks all 928 sub-topics of the UPSC syllabus by what UPSC has asked since 2016. The 60 Prelims Core sub-topics are behind 51% of Prelims questions.

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The same topic in Mains

World physical geographyGS 1 syllabus

Read it in NCERT

Class 11 Fundamentals of Physical Geography, Chapter 8cited in 2 explanations
Class 10 Science, Chapter 5cited in 1 explanation