Which one of the following weeds is particularly effective in controlling water pollution caused by industrial effluents through absorption and accumulation?

Introduction / Context:
Certain aquatic plants are known for their ability to absorb pollutants and heavy metals from water, making them useful in phytoremediation. This question discusses a weed that has been used to reduce water pollution caused by industrial effluents. Recognizing such plants is important in environmental science and pollution control studies.

Given Data / Assumptions:

• The focus is on a weed that controls water pollution from industrial effluents.
• The options are Parthenium, Elephant grass, Water hyacinth, and Mogar grass.
• We assume familiarity with common problem weeds and aquatic plants.

Concept / Approach:
Water hyacinth, an aquatic weed, is notorious for clogging water bodies but is also known for its ability to absorb nutrients and certain pollutants from water. Because of its fast growth and large surface area, it can take up heavy metals and other contaminants, which is why it is sometimes used in wastewater treatment ponds. Parthenium, Elephant grass, and Mogar grass are terrestrial weeds and grasses that do not play a major role in cleaning industrial effluents. Thus, the approach is to identify the aquatic weed used in phytoremediation of water.

Step-by-Step Solution:
Step 1: Recognize that the question refers to water pollution and industrial effluents, suggesting an aquatic plant rather than a land plant. Step 2: Recall that Water hyacinth (Eichhornia crassipes) is a free floating aquatic weed. Step 3: Understand that water hyacinth has been used in some systems to absorb nutrients, organic matter, and certain heavy metals from wastewater. Step 4: Note that Parthenium is a terrestrial weed that invades fields and roadsides and does not grow in water bodies to clean effluents. Step 5: Remember that Elephant grass and Mogar grass are also terrestrial grasses used for fodder or found in fields, not primarily for water pollution control. Step 6: Conclude that Water hyacinth is the weed effective in controlling water pollution from industrial effluents.
Verification / Alternative check:
Environmental case studies on phytoremediation often mention water hyacinth as a plant used in experimental and practical wastewater treatment ponds. Although it is a nuisance in natural water bodies, its ability to absorb various pollutants is well documented. Terrestrial weeds like Parthenium are known more for causing allergies and reducing crop yield than for any environmental cleaning function. This alignment of water hyacinth with wetlands and pollution control technology confirms it as the correct answer.

Why Other Options Are Wrong:
Parthenium: This is an invasive terrestrial weed known for causing health issues in humans and reducing crop yield, not for cleaning water.
Elephant grass: Primarily a fodder grass, it grows on land and is not used for absorbing water pollutants from effluents.
Mogar grass: This is also a land grass and does not play a major role in industrial wastewater phytoremediation.

Common Pitfalls:
Students sometimes focus only on the word weed and ignore the context of water pollution. They may choose Parthenium because it is a famous weed, forgetting that the question specifies water pollution from effluents. To avoid this error, always pay attention to whether the habitat is aquatic or terrestrial. Associating water hyacinth with both water clogging problems and wastewater treatment helps fix this concept in memory.

Final Answer:
The weed effective in controlling water pollution caused by industrial effluents is Water hyacinth.