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# Class 11 Geography NCERT Solutions Chapter 13 Water (Oceans)

Class 11 Geography NCERT Solutions Chapter 13 Water (Oceans)

1. Multiple choice questions.

(i) Identify the element which is not a part of the hydrological cycle

(a) Evaporation
(b) Hydration
(c) Precipitation
(d) Condensation

Explanation: Hydration is not a part of the hydrological cycle. The hydrological cycle, also known as the water cycle, involves processes such as evaporation, condensation, and precipitation, where water is continuously cycled between the Earth’s surface, atmosphere, and back. Hydration refers to the process of adding water molecules to a substance, typically involving the formation of a hydrate compound. It is not a primary process in the hydrological cycle.

(ii) The average depth of continental slope varies between

(a) 2-20m
(b) 200-2,000m
(c) 20-200m
(d) 2,000-20,000m

Explanation: The average depth of the continental slope typically varies between 200-2,000 meters.

(iii) Which one of the following is not a minor relief feature in the oceans:

(a) Seamount
(b) Atoll
(c) Oceanic Deep
(d) Guyot

Explanation: Oceanic Deep is not a minor relief feature in the oceans. It refers to the deep ocean floor areas, including trenches, rather than a specific minor relief feature.

(iv) Salinity is expressed as the amount of salt in grams dissolved in sea water per:

(a) 10 gm
(b) 1,000 gm
(c) 100 gm
(d) 10,000 gm

Explanation: Salinity is typically expressed as the amount of salt in grams dissolved in sea water per 1,000 grams (1 kilogram) of sea water.

(v) Which one of the following is the smallest ocean:

(a) Indian Ocean
(b) Arctic Ocean
(c) Atlantic Ocean
(d) Pacific Ocean

Explanation: The Arctic Ocean is the smallest of the world’s oceans.

(i) Why do we call the earth a Blue Planet?

Ans: The Earth is called a Blue Planet due to its vast water bodies, primarily the oceans, which cover about 71% of its surface. The reflection and scattering of sunlight by water molecules give the planet a blue appearance when viewed from space.

(ii) What is a continental margin?

Ans: A continental margin refers to the zone where a continent’s edge meets the ocean. It includes the continental shelf, continental slope, and continental rise. This region is characterized by varying underwater landforms and geological features.

(iii) List out the deepest trenches of various oceans.

Ans: Some of the deepest ocean trenches include the Mariana Trench (Pacific Ocean), Tonga Trench (Pacific Ocean), Puerto Rico Trench (Atlantic Ocean), Sunda Trench (Indian Ocean), and South Sandwich Trench (Southern Ocean).

(iv) What is a thermocline?

Ans: A thermocline is a layer in the ocean where there is a rapid change in temperature with depth. It separates the warm upper layer (epipelagic zone) from the colder deeper layers and plays a crucial role in ocean circulation and vertical mixing.

(v) When you move into the ocean what thermal layers would you encounter? Why does the temperature vary with depth?

Ans: The temperature profile of oceans across middle and low latitudes can be conceptualized as a three-tiered structure extending from the ocean’s surface to its depths.

The uppermost layer constitutes the warm surface waters, approximately 500 meters thick, with temperatures spanning from 20°C to 25°C. While this tropical layer persists throughout the year, it forms only during summer in mid-latitudes.

Beneath lies the second layer, referred to as the thermocline, characterized by a rapid temperature drop as depth increases. The thermocline’s thickness ranges from 500 to 1,000 meters.

The third stratum, extending to the ocean’s profound depths, is significantly colder. Within the Arctic and Antarctic circles, surface water temperatures approach 0°C, leading to minimal temperature fluctuations as depth increases.

(vi) What is the salinity of sea water?

Salinity refers to the concentration of dissolved salts (primarily sodium chloride) in sea water. It is typically expressed in parts per thousand (ppt) and plays a significant role in ocean density, circulation, and marine ecosystems.