Which of the following is not water-pollinated?

The correct answer is Option (2) → Yucca.

Pollination by water is rare and limited to about 30 genera, mostly monocotyledons. Vallisneria and Hydrilla grow in fresh water, and several marine sea-grasses such as Zostera are also water-pollinated. Yucca is pollinated by an animal, a species of moth.

Option (1) Hydrilla. — Incorrect. Hydrilla is a freshwater plant pollinated by water.

Option (2) Yucca. — Correct. Yucca is pollinated by a moth. The moth lays its eggs in the locule of the ovary, and the flower gets pollinated in turn.

Option (3) Vallisneria. — Incorrect. In Vallisneria the pollen grains are released on the surface of water and carried by water currents to the female flowers.

Option (4) Zostera. — Incorrect. Zostera is a marine sea-grass whose pollen grains are carried inside the water.

NCERT Extract:
Pollination – “… Some examples of water pollinated plants are Vallisneria and Hydrilla which grow in fresh water and several marine sea-grasses such as Zostera.”
Pollination – “… A similar relationship exists between a species of moth and the plant Yucca where both species – moth and the plant – cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower, in turn, gets pollinated by the moth.”