A geographical unit that collects, stores and releases water is called:

1. A

   Watershed

   (a) Watershed. Option (a) states that a geographical unit that collects, stores, and releases water is termed a watershed. This is the exact hydrological definition recognized in geography and environmental science where precipitation runoff is channeled to a common outlet. Therefore, this option is the official key.

2. B

   Wasteland

   (b) Wasteland. Option (b) claims that such a water-collecting geographical unit is a wasteland. Wastelands refer to degraded and unproductive lands rather than functioning hydrological units defined by water collection and release. Hence, this option is incorrect.

3. C

   Wetland

   (c) Wetland. Option (c) asserts that this unit is a wetland. While wetlands are saturated with water, the specific geomorphological unit defined by the collection, storage, and release of runoff across a drainage basin is a watershed. Thus, this option is incorrect.

4. D

   Water reserve

   (d) Water reserve. Option (d) suggests the term water reserve. Water reserves generally denote artificial or natural reservoirs and water bodies rather than the broader geographical drainage unit. Consequently, this option is incorrect.

Summary. Official key is (a) Watershed. A geographical unit that collects, stores and releases water is called a watershed. Other options such as wasteland, wetland, and water reserve refer to different ecological or artificial categories. Students often confuse wetlands with watersheds, but only the watershed defines the integrated drainage basin. Therefore, option (a) is the correct and most precise choice.