Groundwater will not be depleted due to (a) afforestation.
Explanation: Afforestation, the process of planting trees, actually helps replenish groundwater by increasing water infiltration and retention through its root system, making it the only option that does not contribute to depletion.
Why other options are incorrect:
(b) Thermal power plants:
These plants use large amounts of water for cooling, which can significantly deplete groundwater reserves.
(c) Loss of forest, and decreased rainfall:
Forests act as natural water reservoirs, absorbing and storing rainwater. When forests are lost, and rainfall decreases, groundwater levels also deplete.
(d) Cropping of high water demanding crops:
Crops like rice and sugarcane require large amounts of water, which can lead to significant depletion of groundwater reserves when grown extensively.