Group of ten tomato plants are germinated and maintained in a large tray with no drainage. after several weeks they all begin to wilt and die despite repeated watering and fertilization. the most likely cause of this die-off is

If the tomatoes were grown in a place or a kind of soil with no drainage then they are likely to die because one, too much water causes root rotting secondly there is poor circulation of air(oxygen) which is essential for plants survival. Remember air,water, nutrients are essential for growth of plants. Free circulation of air enables the roots to breath.this means that if there is poor drainage of water, there is poor circulation of air.
Why is oxygen important to the roots?
oxygen is necessary for plants to absorb nutrients.It is oxygen that transmits nutrients across the cell wall into the roots.

Reduction in overall biodiversity