Why can plants become weak in waterlogged soil?

Correct answer: Because roots get less air

Plant roots need oxygen for respiration, just as other living parts need energy to function. In waterlogged soil, the spaces between soil particles become filled with water instead of air. Because oxygen moves much more slowly through water than through air, roots may not receive enough oxygen. This can weaken root activity, reduce nutrient absorption, encourage root diseases, and eventually make the whole plant weak. The problem is not excessive sunlight or any change in language or soil value.

Option A is correct because waterlogging reduces the air available around roots. Some plants are adapted to wet conditions, but ordinary crop and land plants may suffer when water remains for too long. The other choices are clearly unrelated to the biological process. The key link to remember is waterlogged soil, less air in the root zone, and weaker plant growth.