Question

Water in lakes and ponds do not freeze at once in cold countries. Give reason.

Answer 1

The specific latent heat of fusion of ice is sufficiently high, about 336 J g^-1. Before freezing the water in the lakes and ponds will have to release a large quantity of heat to the surrounding.  If there is any layer of ice formed on water than water being a poor conductor of heat will also prevent the loss of heat from water of lake. Hence, in cold countries water in lakes and ponds do not freeze.

Answer 2

Since water has a high specific latent heat, it must release a lot of heat into its environment before it can freeze; otherwise,  it will freeze solid all at once.