For a steel boat floating in a lake, the weight of water displaced by the boat is equal to the weight of that part of the boat which is below the surface of the water of the lake (C). This principle is known as Archimedes’ principle. When an object is immersed in a fluid, it displaces an amount of fluid equal to its own weight. In the case of a floating boat, the buoyant force exerted by the displaced water balances the weight of the boat, allowing it to float. This equilibrium occurs because the boat displaces a volume of water equal to its own weight, ensuring that the weight of the water displaced is equal to the weight of the boat. Therefore, the correct option is (C) Equal to the weight of that part of the boat which is below the surface of the water of the lake.