Assertion: Water hyacinth can be vegetatively propagated by offset.
Reason: Water hyacinth is also known as “terror of Bengal”.
A. Both Assertion and Reason are correct and the Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but the Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Hint: Vegetative mode of reproduction is a type of asexual reproduction that can occur through parts of plant like leaves, roots, stems. Specific vegetative parts of the plant undergo regeneration and fragmentation during vegetative reproduction.

Complete Answer:
Water hyacinth is also called Eichhornia crassipes is an aquatic weed that reproduces at an enormous rate. It spreads over the whole water body very quickly and is considered the most invasive weed.

Option B: Offset are the specific parts of the plant that are involved in vegetative reproduction of water hyacinth.
- Offset is a runner that usually originates from the leaf axis of the weed and it runs in a horizontal direction. These offsets have a rosette of leaves below and adventitious roots below them.
- They have an enormous rate of reproduction such that they cover the whole water body and all the other plants and fish below do not get enough sunlight and oxygen respectively, and they eventually die.
- It is called “terror of Bengal” because when the fish dies, the scarcity of fish is experienced by the people of Bengal who eat the fish most in India.
- Thus, though water hyacinth reproduces vegetatively by offset, the reason is not the correct answer for this explanation. Therefore, both Assertion and Reason are correct but the Reason is not the correct explanation for Assertion. Therefore, this is the correct option.

Thus, the correct option is B) Both Assertion and Reason are correct but the Reason is not the correct explanation for Assertion.

Note: The scarcity of fish not only causes lack of food to people in Bengal but also causes financial disturbances to the people as a lot of vendors depend on selling fish to earn their livelihood making the title “terror of Bengal” an apt one.