Explanation:

- Option 1: Groundwater

- Incorrect. The study of groundwater is known as hydrogeology, which focuses on the distribution and movement of groundwater in the soil and rocks of the Earth's crust.

- Option 2: Soil

- Correct. Pedology is the scientific study of soils in their natural environment. It involves understanding soil formation, classification, and mapping, as well as the physical, chemical, and biological properties of the soil.

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- Option 3: Childhood illness

- Incorrect. The study of childhood illnesses falls under the category of pediatrics, which deals with the medical care of infants, children, and adolescents.

- Option 4: Skin disease

- Incorrect. Dermatology is the branch of medicine that focuses on skin diseases, dealing with the skin's health and diseases affecting skin, hair, and nails.

Pedology plays an essential role in agriculture, environmental sciences, and land planning.