The correct option is C 4∘
Water exhibits an anomalous behaviour; it contracts on heating between 0oC and 4oC. When the surface of the lake cools down above 4oC the cool water at the surface flows to the bottom because of its greater density. But when the surface temperature reaches to 2oC, the water near the surface is less dense than the warmer water below. Hence the downword flow ceases, and the water near the surface remains colder than that at the bottom.
So the temperature expected at the bottom is 4oC
option (C) is the correct answer.