In Vallisneria, the pollination is carried by :

The correct answer is Option (2) → Water

Option (2) Water — Correct. In Vallisneria the female flower reaches the water surface on a long stalk, and the male flowers or pollen released on the water are carried to it by currents.

NCERT Extract:
Pollination – “… As against this, you would recall that water is a regular mode of transport for the male gametes among the lower plant groups such as algae, bryophytes and pteridophytes. It is believed, particularly for some bryophytes and pteridophytes, that their distribution is limited because of the need for water for the transport of male gametes and fertilisation. Some examples of water pollinated plants are Vallisneria and Hydrilla which grow in fresh water and several marine sea-grasses such as Zostera.”