The rock which has the capacity to retain underground water is?

1. Analyze the question The question asks which type of rock can retain (hold and store) underground water. This is about aquifers and groundwater.

2. Explain the concept

• Permeable rocks have pores or cracks that let water pass through and be stored. Examples are sandstone, limestone, gravel and chalk. A permeable rock that holds water is called an aquifer.
• Impermeable rocks have no connected pores, so water cannot pass through them. Examples are clay, shale and granite. They act as barriers that stop water from sinking deeper.
• Crystalline rocks (such as granite and gneiss) are tightly interlocked and usually hold very little water unless they are fractured.
• Compact rocks are densely packed with very few spaces, so they store little water.

3. Step-by-step solution

1. Retaining underground water requires spaces in the rock where water can enter and be stored.
2. Only rocks with connected pore spaces allow water to enter, and these are permeable rocks.
3. Impermeable, crystalline and compact rocks have few or no usable spaces, so they cannot hold much water.
4. Therefore, the rock that can retain underground water is permeable.

4. Answer The correct option is D. permeable.

(Note: Some students pick A because impermeable rock "holds" water on the surface, like clay in ponds. The question asks about underground water storage, which needs permeable rock.)

5. Exam tip Remember: Permeable = Passes water in and stores it (aquifer). Impermeable = Prevents passage. Wells and boreholes are drilled into permeable rock layers that sit above an impermeable layer.