I have worked in this organization for five years trying to check the erosion of ethical values.

Answer: Option B

Decay : (of organic matter) rot or decompose through the action of bacteria and fungi.
Corrosion : damage caused to metal, stone, or other materials by corrosion.
Misuse : use (something) in the wrong way or for the wrong purpose.
Expansion : the action of becoming larger or more extensive.
Erosion : the gradual destruction or diminution of something.

Synonym of Erosion is Corrosion