World's most problematic aquatic weed is:

The correct answer is Option (3) → Eichhornia crassipes

Option (1) Free floating algae — Incorrect. Free-floating algae form algal blooms in polluted water and harm it, but NCERT names water hyacinth, a flowering plant, as the most problematic weed.

Option (2) Vallisneria — Incorrect. Vallisneria is a submerged water plant known for pollination by water. It is not a weed problem.

Option (3) Eichhornia crassipes — Correct. Water hyacinth grows fast in water bodies rich in nutrients and chokes them.

Option (4) Chara — Incorrect. Chara is a green alga of freshwater ponds; it is not a problematic weed.

Note 1: A similar question was also asked in CUET (UG) 2023 on 13-06-2023 (Slot 3) and on 09-06-2023 (Slot 3).

Note 2: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Domestic Sewage and Industrial Effluents – “… You may have seen 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’.”