Pycnocline is a layer in the oceanic body in which the density of water increases with the depth in the ocean. This change in density happens due to the changes in temperature and salinity of water.
<u>Other four words/phrases are related to the process of water purification. The only word which does not fit in the water purification process is Pychnocline. </u>
A famous quote of MLK is: "Nonviolence is a powerful and just weapon. which cuts without wounding and ennobles the man who wields it. It is a sword that heals." This is why I believe that is the answer.
