Adecrease in entropy is associated with which type of reaction

A decrease in entropy is associated with Anabolic reactions. 
Anabolic reactions are powered by catabolism where large molecules are broken down into smaller parts and then used up in cellular respiration. Many anabolic processes are powered by the hydrolysis of ATP. Living organisms are able to make highly ordered structures by coupling free energy- yielding catabolic processes ( increase in entropy) with energy requiring anabolic processes (decrease entropy).

Decomposition is the cycle at which bacteria breaks down any organic material into the soil