Correct Option
The correct option isThe expulsion of air dissolved in the water.
Explanation
When water is heated below its boiling point, physical changes related to solubility of gases occur before the phase transition to vapor begins.
Statement-wise Analysis
- The breakdown of water molecules into hydrogen and oxygen: Incorrect. Such decomposition requires electrolysis or extremely high temperatures, not ordinary heating.
- The expansion of the container material: Incorrect. Expansion of the container does not produce bubbles within the water.
- The expulsion of air dissolved in the water: Correct. As temperature increases, the solubility of gases in water decreases, causing dissolved air to come out as bubbles on the container surface.
- The formation of steam due to localized boiling: Incorrect. Steam formation occurs at the boiling point; the observed bubbles appear before boiling.
Key Takeaway: Heating water below its boiling point releases dissolved gases, producing bubbles before vaporization begins.