Step-by-step explanation:
When a large block of ice is placed in a hot cup of water then some of the ice will melt into the cup. As a result, when ice melts then after sometime temperature of cup will become equal to the temperature of ice.
Therefore, ice won't melt further as surface area of cup is small so, only some of the ice will melt into it.
Whereas when same block melts when dropped into a lake it completely melts because lake has large surface area and hence, ice will melt into it easily. This is also because there is different in temperature of both ice and lake.
So, ice will melt into it as temperature of ice will be less than the temperature of lake.