Consider the following statements regarding the "air in water": 1. It is essential for aquatic animals. 2. It cannot be removed even by boiling the water. 3. It is visible as bubbles when water is heated but not boiling. Which of the statements given above is/are correct?

The correct option is (c) 1 and 3 only Explanation Water bodies contain dissolved air, primarily oxygen and nitrogen, which is physically mixed with water molecules. The solubility of these gases is influenced by temperature and pressure. This dissolved air is a critical abiotic factor sustaining life in aquatic ecosystems. Statement-wise Analysis - Statement 1 is Correct: Aquatic animals, such as fish, rely on the oxygen dissolved in water for respiration. They use specialized organs like gills to extract this dissolved oxygen directly from the water. Without dissolved air, most aquatic animal life cannot survive. - Statement 2 is Incorrect: The solubility of gases in liquids decreases as temperature increases. When water is boiled, the increased temperature causes the dissolved air to escape into the atmosphere. Consequently, boiled and cooled water is oxygen-deficient and often tastes "flat." - Statement 3 is Correct: When water is heated, but before it reaches its boiling point, small bubbles are observed forming on the inner surface of the vessel. These bubbles consist of the air that was dissolved in the water, which comes out of the solution as the temperature rises and solubility decreases. Key Takeaway: Dissolved oxygen is essential for aquatic respiration. The solubility of gases in water is inversely proportional to temperature; heating water expels dissolved air even before the boiling point is reached.

NCERT Class 6 Environment & Ecology — Chapter 2: Air around us

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Consider the following statements regarding the "air in water":

It is essential for aquatic animals.
It cannot be removed even by boiling the water.
It is visible as bubbles when water is heated but not boiling.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

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

Did you get this right?

Solution

The correct option is (c) 1 and 3 only

Explanation

Water bodies contain dissolved air, primarily oxygen and nitrogen, which is physically mixed with water molecules. The solubility of these gases is influenced by temperature and pressure. This dissolved air is a critical abiotic factor sustaining life in aquatic ecosystems.

Statement-wise Analysis

Statement 1 is Correct: Aquatic animals, such as fish, rely on the oxygen dissolved in water for respiration. They use specialized organs like gills to extract this dissolved oxygen directly from the water. Without dissolved air, most aquatic animal life cannot survive.
Statement 2 is Incorrect: The solubility of gases in liquids decreases as temperature increases. When water is boiled, the increased temperature causes the dissolved air to escape into the atmosphere. Consequently, boiled and cooled water is oxygen-deficient and often tastes "flat."
Statement 3 is Correct: When water is heated, but before it reaches its boiling point, small bubbles are observed forming on the inner surface of the vessel. These bubbles consist of the air that was dissolved in the water, which comes out of the solution as the temperature rises and solubility decreases.

Key Takeaway: Dissolved oxygen is essential for aquatic respiration. The solubility of gases in water is inversely proportional to temperature; heating water expels dissolved air even before the boiling point is reached.

Your note

More from Chapter 2: Air around us

Consider the following statements regarding the atmosphere: 1. It is a thin layer of air that surrounds the earth. 2. It extends only up to 10 km above the surface of the earth. 3. The air becomes denser as we move higher in the atmosphere. Which of the statements given above is/are correct?

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With reference to the composition of air, consider the following statements: 1. Nitrogen and oxygen together make up approximately 99% of the air. 2. Carbon dioxide constitutes the majority of the remaining 1% of air. 3. The composition of air varies from place to place. Which of the statements given above is/are correct?

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Consider the following statements regarding water vapour in the air: 1. Air contains water vapour only during the rainy season. 2. When air comes in contact with a cool surface, water vapour condenses. 3. The presence of water vapour in air is essential for the water cycle in nature. Which of the statements given above is/are correct?

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With reference to the burning of fuel and its by-products, consider the following statements: 1. Burning can occur in the absence of oxygen if nitrogen is present. 2. Burning of fuel produces smoke which contains a few gases and fine dust particles. 3. Smoke produced by burning fuel is generally beneficial to respiratory health. Which of the statements given above is/are correct?

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Consider the following statements regarding the "dust particles" in the air: 1. Dust particles are always present in the air. 2. The presence of dust particles in air is constant irrespective of time and place. 3. Breathing through the mouth can allow harmful dust particles to enter the body. Which of the statements given above is/are correct?

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The correct option is (c) 1 and 3 only

Explanation

Statement-wise Analysis

Statement 1 is Correct: Aquatic animals, such as fish, rely on the oxygen dissolved in water for respiration. They use specialized organs like gills to extract this dissolved oxygen directly from the water. Without dissolved air, most aquatic animal life cannot survive.
Statement 2 is Incorrect: The solubility of gases in liquids decreases as temperature increases. When water is boiled, the increased temperature causes the dissolved air to escape into the atmosphere. Consequently, boiled and cooled water is oxygen-deficient and often tastes "flat."
Statement 3 is Correct: When water is heated, but before it reaches its boiling point, small bubbles are observed forming on the inner surface of the vessel. These bubbles consist of the air that was dissolved in the water, which comes out of the solution as the temperature rises and solubility decreases.