The length of time required for half of the radioactive atoms in a sample to decay is its

HALF LIFE.

Explanation:

The half life of a radioactive element refers to the length of time that is required for the half of the atoms of a particular sample of radioactive element to decay. For instance a radioactive element that a mass of 120 g and a half life of 2 years will be reduce to 60 g in two years. Half life is usually used to measure the rate of disintegration of an unstable isotope. The principle of half life of radioactive elements can be used to determine the relative ages of rocks.  

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.