World's most problematic aquatic weed is:

Eichhornia crassipes

The correct answer is Option (3)- Eichhornia crassipes

The beautiful mauve-colored flowers found on very appealingly-shaped floating plants in water bodies. These plants which were introduced into India for their lovely flowers have caused havoc by their excessive growth by causing blocks in our waterways. They grow faster than our ability to remove them.

These are plants of water hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed, also called ‘ Terror of Bengal ’. They grow abundantly in eutrophic water bodies, and lead to an imbalance in the ecosystem dynamics of the water body.