The acidification of oceans is increasing. Why is this phenomenon a cause of concern? 1. The growth and survival of calcareous phytoplankton will be adversely affected. 2. The growth and survival of coral reefs will be adversely affected. 3. The survival of some animals that have phytoplanktonic larvae will be adversely affected. 4. The cloud seeding and formation of clouds will be adversely affected. Which of the statements given above is/are correct?

The acidification of oceans is primarily caused by the absorption of excess atmospheric carbon dioxide (CO₂) by seawater. This absorption leads to a decrease in ocean pH and a reduction in the concentration of carbonate ions (CO₃²⁻), which are essential for many marine organisms to build their shells and skeletons. Correct Option Statements 1, 2, and 3 correctly identify the concerns associated with ocean acidification. - Statement 1: Calcareous phytoplankton, such as coccolithophores, form shells composed of calcium carbonate (CaCO₃). The decrease in carbonate ion availability due to ocean acidification makes it more difficult for these organisms to form and maintain their shells, adversely affecting their growth and survival. - Statement 2: Coral reefs are built by coral polyps that secrete calcium carbonate skeletons. Ocean acidification reduces the saturation state of aragonite and calcite (forms of CaCO₃), hindering the calcification process. This can lead to slower coral growth, increased erosion, and greater susceptibility to bleaching, thereby threatening the survival of coral reefs. - Statement 3: Many marine animals, including mollusks, crustaceans, and echinoderms, have larval stages that rely on calcification for the development of their shells or skeletal structures. The altered ocean chemistry caused by acidification can impair the formation and maintenance of these structures during critical early developmental stages, adversely affecting their survival. Incorrect Options - Statement 4: Cloud seeding and the formation of clouds are atmospheric processes primarily influenced by factors such as atmospheric aerosols, water vapor concentration, and temperature. Ocean acidification, which relates to the chemical changes in seawater, does not have a direct or significant impact on these atmospheric phenomena. Therefore, this statement is incorrect. - Option (b) 2 only: This option is incorrect because statements 1 and 3 are also valid concerns related to ocean acidification. - Option (c) 1 and 3 only: This option is incorrect because statement 2, concerning coral reefs, is a major and well-documented impact of ocean acidification. - Option (d) 1, 2, 3 and 4: This option is incorrect because statement 4 is factually inaccurate regarding the impacts of ocean acidification.

IAS 2012 — Environment & Ecology Environment & Ecology

2012mcqmedium

The acidification of oceans is increasing. Why is this phenomenon a cause of concern?

The growth and survival of calcareous phytoplankton will be adversely affected.
The growth and survival of coral reefs will be adversely affected.
The survival of some animals that have phytoplanktonic larvae will be adversely affected.
The cloud seeding and formation of clouds will be adversely affected.

Which of the statements given above is/are correct?

Official previous-year question

Verified 2 Aug 2026.

Options

A1, 2 and 3 only
B2 only
C1 and 3 only
D1, 2, 3 and 4

Did you get this right?

Solution

The acidification of oceans is primarily caused by the absorption of excess atmospheric carbon dioxide (CO₂) by seawater. This absorption leads to a decrease in ocean pH and a reduction in the concentration of carbonate ions (CO₃²⁻), which are essential for many marine organisms to build their shells and skeletons.

Correct Option

Statements 1, 2, and 3 correctly identify the concerns associated with ocean acidification.

Statement 1: Calcareous phytoplankton, such as coccolithophores, form shells composed of calcium carbonate (CaCO₃). The decrease in carbonate ion availability due to ocean acidification makes it more difficult for these organisms to form and maintain their shells, adversely affecting their growth and survival.
Statement 2: Coral reefs are built by coral polyps that secrete calcium carbonate skeletons. Ocean acidification reduces the saturation state of aragonite and calcite (forms of CaCO₃), hindering the calcification process. This can lead to slower coral growth, increased erosion, and greater susceptibility to bleaching, thereby threatening the survival of coral reefs.
Statement 3: Many marine animals, including mollusks, crustaceans, and echinoderms, have larval stages that rely on calcification for the development of their shells or skeletal structures. The altered ocean chemistry caused by acidification can impair the formation and maintenance of these structures during critical early developmental stages, adversely affecting their survival.

Incorrect Options

Statement 4: Cloud seeding and the formation of clouds are atmospheric processes primarily influenced by factors such as atmospheric aerosols, water vapor concentration, and temperature. Ocean acidification, which relates to the chemical changes in seawater, does not have a direct or significant impact on these atmospheric phenomena. Therefore, this statement is incorrect.
Option (b) 2 only: This option is incorrect because statements 1 and 3 are also valid concerns related to ocean acidification.
Option (c) 1 and 3 only: This option is incorrect because statement 2, concerning coral reefs, is a major and well-documented impact of ocean acidification.
Option (d) 1, 2, 3 and 4: This option is incorrect because statement 4 is factually inaccurate regarding the impacts of ocean acidification.

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Correct Option

Statements 1, 2, and 3 correctly identify the concerns associated with ocean acidification.

Statement 1: Calcareous phytoplankton, such as coccolithophores, form shells composed of calcium carbonate (CaCO₃). The decrease in carbonate ion availability due to ocean acidification makes it more difficult for these organisms to form and maintain their shells, adversely affecting their growth and survival.
Statement 2: Coral reefs are built by coral polyps that secrete calcium carbonate skeletons. Ocean acidification reduces the saturation state of aragonite and calcite (forms of CaCO₃), hindering the calcification process. This can lead to slower coral growth, increased erosion, and greater susceptibility to bleaching, thereby threatening the survival of coral reefs.
Statement 3: Many marine animals, including mollusks, crustaceans, and echinoderms, have larval stages that rely on calcification for the development of their shells or skeletal structures. The altered ocean chemistry caused by acidification can impair the formation and maintenance of these structures during critical early developmental stages, adversely affecting their survival.

Incorrect Options

Statement 4: Cloud seeding and the formation of clouds are atmospheric processes primarily influenced by factors such as atmospheric aerosols, water vapor concentration, and temperature. Ocean acidification, which relates to the chemical changes in seawater, does not have a direct or significant impact on these atmospheric phenomena. Therefore, this statement is incorrect.
Option (b) 2 only: This option is incorrect because statements 1 and 3 are also valid concerns related to ocean acidification.
Option (c) 1 and 3 only: This option is incorrect because statement 2, concerning coral reefs, is a major and well-documented impact of ocean acidification.
Option (d) 1, 2, 3 and 4: This option is incorrect because statement 4 is factually inaccurate regarding the impacts of ocean acidification.