Answer: Option A. -> ocean, land
:
A
The circulation of water between ocean and land is known as the water cycle. The energy required for this process is provided primarily by the sun. Evaporation and condensation of water plays an important role in water cycle.

Answer: Option B. -> Saline water > Frozen water > Usable surface water
:
B

Since oceans (which is saline in nature) are the biggest reservoir of water, containing about 97% of all the water present on the earth, these are the most available form of water on the earth. The second source of water, i.e., frozen water or ice is found on poles and mountains. The ice melts and feeds all the rivers which represent the usable surface water. Hence, the correct order is Saline water > Frozen water > Usable surface water

Answer: Option B. -> Water cycle
:
B
Drying of water under sunlight is an example of evaporation of water. This is phenomenon X.
The water vapours present in air outside the surface of the cold glass of water get condensed due to cooling. The conversion of vapours into liquid is known as condensation.This is phenomenon Y. 
The two phenomena play an important role in the water cycle.

Answer: Option C. -> Collisions of celestial bodies with the earth.
:
C
Both comets and asteroids can contain ice. Some scientists suspect that such bodies could easily have delivered water leading to the formation of oceans.
Other scientists believe that meteoroids hit the Earth and led to the origin of water.

Answer: Option B. -> Amount of infiltration > Amount of ground water used
:
B
If the amount of water that is fed underground is more than the usage, it will lead to an increase in the groundwater level. This is achieved by taking steps like reduction of unnecessary water, keeping check on the usage of water by industries, prohibiting the release of effluents and toxic chemicals in water, etc.

Answer: Option A. -> Conservation of water
:
A and C
Rainwater harvesting is a technique used for collecting, storing and using rainwater. It can be done for groundwater refilling or for conserving water for day-to-day use.
During rainfall, water is stored on the top of rooftops and concrete roads. This water is guided via pipes to be stored in tanks or reservoirs for future use. It can be made to seep through the ground so as to increase the underground water level.

Answer: Option A. -> Conservation of water
:
Groundwater is the water located beneath the earth's surface in soil and in the fractures of rock formations.

Answer: Option A. -> Conservation of water
:

1 Mark each
Some steps to conserve groundwater are as follows:
1. All chemicals should be adequately disposed of.
2. The amount of fertilisers used on plants should be limited.
3. The sewage pipes should be free from leakage.
Chemicals, fertilisers and other toxic substances if not properly used can infiltrate to the groundwater and contaminate it.

Answer: Option A. -> Conservation of water
:

1 Mark each
[Mention any three]

Water is an essential source for the existence of life. Some ways in which we can conserve water are as follows:
1. Avoiding water wastage is also a kind of water conservation.
2. Dams can be built to store excess rainwater running in the river.
3. Drinking water should not be wasted to water the plants.
4. Water should not be wasted during irrigation of fields. Modern methods like spraying, sprinkling or drip irrigation should be used.
5. Water should be used judiciously to avoid wastage.

Answer: Option A. -> Conservation of water
:

Naming: 0.5 Marks each.
[Mention any 4]
The conventional methods used for the purification of water are as follows:

1. Boiling


2. Sedimentation


3. 3 pole system of filtering


4. Sieving through muslin cloth


5. Using Alum


6. Chlorination