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.