Final answer:
Lakes freeze at the surface because ice is less dense than liquid water, which allows it to float and insulate the water below. This insulating layer is essential for the survival of aquatic life during winter, as it prevents entire lakes from freezing solid.(Option b)
Step-by-step explanation:
Lakes only freeze at the surface because ice is less dense than liquid water. When water cools down and ice forms, it floats on the surface due to this lower density. This phenomenon plays a crucial role in the survival of aquatic life, as the layer of ice insulates the water beneath, preventing the entire body of water from freezing.
Water reaches its maximum density at approximately 4°C. Below this temperature, water expands as it cools further and freezes. If ice sank as it formed, bodies of water would freeze from the bottom up, endangering aquatic ecosystems. But because ice floats, liquid water remains underneath, allowing many organisms to live through the winter.