Hydrology is the science which deals with 1: rain water 2: river water 3: sea water 4: surface and underground water

4: surface and underground water

Hi Alex,

This is not my area of expertise, but this explanation from

Wikipedia  I consider as to be a good answer:

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans isoceanography. Ecological processes with hydrology are in focus ofecohydrology.

The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is1,338,000,000 km3 (321,000,000 mi3).[2]

Liquid water is found in bodies of water, such as an ocean, sea, lake, river,stream, canal, pond, or puddle. The majority of water on Earth is sea water. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers.

Water is important in many geological processes. Groundwater is present in most rocks, and the pressure of this groundwater affects patterns of faulting. Water in the mantle is responsible for the melt that produces volcanoes atsubduction zones. On the surface of the Earth, water is important in both chemical and physical weathering processes. Water, and to a lesser but still significant extent, ice, are also responsible for a large amount of sediment transport that occurs on the surface of the earth. Deposition of transported sediment forms many types of sedimentary rocks, which make up the geologic recordof Earth history(wЊkipedia)

Surface and underground water, in different layers

I will go with4 as it the correct answer.

Option -4- is the best answer

Hydro means under earth so Hydrology is the science which deals with surface and underground water

Answer  :4   Surface  and underground  water                                                                  .                                                     .

 The Hydrology relates to the existence of water on the earth surface. So No.4 is the answer.

I agree with Jacob Alomer

all of the above, when water is  a vapour, thn falls as rain, thn moving in rivers ocean sea...