Pesticides are a mixture of two or more substances. They are used for killing pests. Pests include insects, plant pathogens, weeds, mollusks, etc., that destroy the plant crop and spread diseases. Aldrin and dieldrin are the names of some common pesticides Herbicides are pesticides specially meant for killing weeds. For example, sodium chlorate (NAClO3), sodium arsenite (Na3AsO3), etc.