During the cold winter months, the surface of a lake becomes hard ice. this is due to which change of state? condensation evaporation melting freezing

Freezing

Explanation:

During cold winter months, the water on the surface of lakes/water bodies changes its state from liquid to solid state (ice) and the process is known as freezing. This phenomenon helps the flora and fauna living under such water bodies survive even in extremely cold weather. The ice being less dense than water floats on the surface of lake and acts as a shield. This shield of ice acts as an insulator and restricts the outside cold waves from entering the water beneath the ice cover and maintains optimum temperature inside. Hence due to the change of state of water, the flora and fauna is able to survive even in harsh winter season.  

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.