(a) Isobath - An imaginary line on a map joining the points of equal depths.
(b) Isohaline - An imaginary line on a map joining the points of equal salinity in oceans.

(a) Water table is a level below the ground, where water is found collected beneath the Earth's surface.
(b) Aquifers are porous rock strata filled with water, found below the earth's surface.

(i) One of the most indispensable natural resources on earth is water.
(ii) The Earth is also called the Blue planet, as it holds water in abundance.
(iii) Thus stands unique among all other planets

(i) The earth consists of four spheres
(ii) They are a) Lithosphere,
b) Atmosphere,
c) Hydrosphere and
d) Biosphere

(i) The degree of concentration of salts in the sea water is called salinity.
(ii) It is usually expressed in terms of parts per thousand (ppt or %0).
(iii) Salinity varies both horizontally and vertically.
(iv) The influence of temperature on ocean salinity depends upon the heating up of the surface water, which varies from tropics to polar regions

The factors that generate ocean currents are:
(i) Earth's rotation
(ii) Prevailing winds and
(iii) Differences in temperature and salinity of ocean water

(i) The Earth's water is not static.
(ii) It is always in motion.
(iii) This continuous movement of water on, above and below the earth's surface is called the Hydrological Cycle.
(iv) The three major processes involved in the water cycle are evaporation, condensation and precipitation.

(i) Salt in the ocean comes from rocks on land.
(ii) The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic due to carbonic acid (which forms from carbon dioxide and water).
(iii) As the rain erodes the rock, acids in the rainwater break down the rock. This process creates ions, or electrically charged atomic particles. These ions are carried away in run off to streams and rivers and ultimately to the ocean.
(iv) Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not used up and are left for long periods of time where their concentrations increase over time.
(v) Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up over 90 percent of all dissolved ions in the ocean. Sodium and Chloride are 'salty'. So, the oceans are salty

(i) The biotic and abiotic resources found in the oceanic water and at the bottoms are called manne resources.
(ii) Fishes, plankton, sea grass, coral, etc are biological resources.
(iii) Petioleum, Natural gas, Metallic Minerals, Sand, gravet, etc, are mineral resources.
(iv) Energy fuels, Tidal energy, wave energy, etc, are energy resources.
Influence:
(i) The ocean's resources play a vital role in sustaining the needs of society.
(ii) A diverse array of marine organisms is used for food, medicine, cosmetics, and a wealth of industrial applications.
(iii) The world's demand for energy, minerals and water have become increasingly dependent on non-living marine resources.

C) A is correct but R is false.

A) both A and R are correct and R explains A.

The Arabian sea nestled up against the dry middle East, appears much saltier than the neighbouring Bay of Bengal which gets showered by intense monsoon rains and receives fresh water discharges from the Ganges and other large rivers.

(i) They are shallower, thus enables sunlight to penetrate through the water.
(ii) This encourages abundant growth of grass, sea weeds and plankton.
(iii) Hence these zones become the richest fishing grounds.

(i) After years and years of river inflow and evaporation, the salt content of the lake water built up to the present levels.
(ii) The same process made the seas salty.
(iii) Rivers carry dissolved salts to the ocean.
(iv) Water evaporates from the oceans to fall again as rain and to feed the rivers, but the salt remains in the oceans.
Therefore the ocean waters are saline in nature.

(i) The Northern Hemisphere holds 61% of land.
(ii) The Southern Hemisphere holds 81% of water. .
(iii) It is because of this pattern of land and water distribution, the Northern hemisphere is called as the land hemisphere and the Southern hemisphere is called as the water hemisphere.