Step 1: Understanding 'Terror of Bengal'.
Water hyacinth (\textit{Eichhornia crassipes}) is an invasive aquatic weed. It clogs water bodies, depletes oxygen, and hampers aquatic biodiversity.
Step 2: Reason for the name.
It spreads rapidly in Bengal’s water bodies, causing serious ecological and economic problems, hence called the "Terror of Bengal".
Step 3: Conclusion.
Thus, the correct plant is Water hyacinth.