The unwanted plants which grow in field along with the crop plants are termed as weed. They are harmful for the crops as they compete for nutrients with them.
The Eichhornia , commonly known as common water hyacinth, is an aquatic plant native to the Amazon basin, and is often a highly problematic invasive species outside its native range . It grows at an alarming rate and spreads on the surface of the water body. This cut out of the light and it also causes an increase in the oxygen demand. Thus, causing the death of fishes and other aquatic organisms.
Parthenium hysterophorus is commonly called as congress grass or gajar ghass .It is a species of flowering plant in the aster family, Asteraceae. It is native to the American tropics. This weed is equally dangerous for all flora and fauna. It is highly dangerous for humans. It utilizes most of the nutritious substances from soils, thus converting fertile ground into unfertile ones.
So the correct answer is 'Parthenium hysterophorus'
Agent Orange refers to a herbicide mixture which was used by the U.S. military during the Vietnam War and it contained a dangerous chemical contaminant called dioxin.
The active ingredient of Agent Orange was an equal mixture of two phenoxy herbicides – 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5 trichlorophenoxyacetic acid (2,4,5-T) and it also contained traces of the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).