Freezing refers to the phase change from liquid to solid phase.

In this case, we are discussing the freezing of water. Water freezes at 0 degrees Celsius. Since no other information is given, let us assume that the water is already at 0 degrees Celsius and is going to freeze.

The amount of heat released when the water freezes is also known as the latent heat of fusion and is equal to 80 calories per gram of water or, 334 Joules per gram of water.

Here we have 100 grams of water.

Thus, the amount of heat released on freezing = mass of water x latent heat of fusion.

= 100 g x 334 J/g = 33,400 J = 33.4 kJ 

Thus, 33.4 kilojoules of energy is released when 100 g of water freezes. 

Hope this helps.