Mechanism of heat-transfer involved in freezing of lakes in colder region:

Explanation

Initially, the water in the lake is cooled by convection as colder air makes contact with the water's surface, causing the surface water to cool, become denser, and sink. This process continues until the temperature of the water reaches approximately 4ºC. Once the surface water begins to freeze, a layer of ice forms, and the primary heat transfer mechanism becomes conduction. The ice layer acts as an insulator, and any further heat loss from the water beneath the ice occurs through conduction. Therefore, the correct answer is 'Conduction only.'Convection only is incorrect because convection only dominates until the initial cooling phase. Radiation only is incorrect because radiation is not the main mechanism involved in the freezing process. None of these is incorrect because conduction is indeed the correct mechanism after the initial convection phase.