Answer: Option D. -> Drip irrigation
:
D

Drip irrigation is a type of irrigation in which plants are watered by using narrow tubings, which deliver the water to the plant slowly and directly to the base of the plant. This reduces the total amount of water required for agriculture and, hence helps in water conservation.

Answer: Option C. -> Excessive use of groundwater and shortage of rainfall
:
C

Groundwater depletion is observed when the groundwater overconsumption is not constantly replenished by water bodies like lakes and flowing rivers or rainfall. Hence, both the shortage of rainfall and excessive use of groundwater will lead to depletion of water table.

Answer: Option A. -> True
:
A

Humans have been blessed with groundwater but lately, due to mismanagement of this boon, we have started facing acute shortage of freshwater, which results in the depletion of the water table.

Answer: Option A. -> Water table decreases
:
A

With the increase in population, the demand for groundwater increases as every human being needs a minimum amount of water for his/her sustenance and daily activities. Thus, the water table eventually decreases.
However, we can adopt techniques such as rainwater harvesting to maintain the level of groundwater.

Answer: Option B. -> False
:
B

The water table is at different depths in different places. For instance, to reach the water table in Rajasthan one might have to dig around 20 feet into the ground whereas one will have to dig around 10 feet only in Meghalaya.

Answer: Option D. -> Oceans
:
D

Freshwater is the name given to the part of water available on earth which is not salty and is fit for use. Rivers, polar ice caps and groundwater all fall under the category of freshwater. Oceans on the other hand contain salty water. Hence, oceans are not a source of freshwater.

Answer: Option C. -> X:- Evaporation, Y:- Precipitation
:
C

Evaporation (X):- It is a phase transition in which the liquid converts into gas. For example, water converts into water vapour.

Precipitation (Y):- After the condensation of water vapour, it falls on the surface of the earth. Most of the precipitation occurs in the form of rain, but also includes snow, hail etc.

The figure represents the water cycle, which also includes condensation (the process in which the evaporated water vapour converts to liquid water droplets in the air, forming clouds).

The sequence of processes is:
Evaporation $\to$ Condensation $\to$ Precipitation

Answer: Option B. -> Most of the available water is salty and unfit for consumption.
:
B

Though, about 71% of the Earth’s surface is covered with water, we still face water shortages because most of the water is available in oceans. This water is salty and cannot be used for our day to day activities. 
The water in lakes and rivers is also getting polluted everyday. The level of groundwater is also going down. We need to make sure that we use water judiciously so that freshwater is available for everyone.
We can adopt techniques such as rainwater harvesting so that we can save rainwater for future use.

Answer: Option C. -> Lake water < Well water < Rainwater
:
C
Rainwater is the purest form of natural water. Water from the water bodies such as lakes, ponds get evaporated leaving behind the impurities. The condensed water vapour is the most pure form of water among all the sources of natural water. 
Underground is next only to rainwater in terms of purity. It contains dissolved impurities.
River and lake water contains dissolved impurities like salts, and insoluble impurities like clay, sand and living organisms (including microbes).
Therefore, the correct of purity from the given water sources is:
Lake water < Well water < Rainwater

Answer: Option A. -> True
:
A

Agricultural activities needs a significant quantity of water for irrigation purposes, most of which comes from groundwater. Increasing population means increase need for agriculture and this, in turn, puts more pressure on the groundwater level. Hence, the groundwater is being used at an increasing rate which is causing the depletion of the water table.