Answer: Option A. -> 0.006%
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A
Though 71% of the Earth's total surface is covered with water, it is largely in the form ofoceans and seas.Thiswater is saltyandcannot be used fordaily activities by humans. Only 2.5-2.75% is fresh water, including 1.75-2%, isfrozen in glaciers, ice and snow, 0.5-0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.And of this fresh water, the actual amount of water that is directly available and safe for usefor humans, i.e., usable freshwater,is only around 0.006%.

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Explanation: 2 Marks
When freshwater freezes, water molecules of hydrogen and oxygen bond together into a crystalline form called ice. In seawater, the presence of salt makes it harder for water molecules to bond to the icestructure because ice naturally repels salt molecules. So in a sense, the salt gets in the way of water molecules, blocking them from joining together to form ice.

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Naming: 0.5 Mark each.
The conventional methods used for the purification of water are as follows:

1. Boiling


2. Sedimentation


3. Using Alum


4. Chlorination

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Definition: 1 Mark
Reasoning out: 1 Mark
Explanation 1 Mark
Turbidityis the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in the air. The measurement ofturbidityis a key test ofwaterquality.
The turbidity of water is based upon a comparison of the amount of light passing through a given water sample with that passing through a standard sample. Usually, this is defined in terms of the depth of water to which a candle flame can be clearly distinguished.
Turbidityis caused by particles suspended or dissolved inwaterthat scatter light making thewaterappear cloudy or murky. Particulate matter can include sediment - especially clay and silt, fine organic and inorganic matter, soluble colored organic compounds, algae, and other microscopic organisms.

Answer: Option C. -> Rain water
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C
Rainwater is the purest form of natural water. It is formed naturally by evaporation followed by condensation of water vapour.
Underground is next to rainwater in terms of purity as it contains dissolved impurities followed by river and ocean water.

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Measures: 5Marks
There are many ways to solve the water shortage of thevillage.
1) The villagers should use modern irrigation methods like drip irrigation where water is supplied to the plants via an underground network of pipes. This saves water by supplying water directly to the roots and also inhibits wastage due to ground evaporation.
2) Deforestation or clearing of forests further increases wastage of water because tree roots hold rainwater and allow proper infiltration. In absence of trees, the rainwater will run off easily. So, the villagers should plant more and more trees.
3) Moreover, in order to solve the problem of drought, the villagers should build water collection tanks like Bawris or ponds.
4) Rainwater harvesting can also be done by the people where the rainwater is stored and used judiciously by the help of a network of pipes and tanks.
5) Household water can be used for watering plants.

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Explanation: 3 Marks
Normal behavior for a liquid is to expand on heating and contract on cooling. A liquid that contracts is said to become denser.
Water behaves like a normal liquid when it's cooled down to 4 degrees(it contracts). But when cooled further down from 4 degrees to 0 degrees, it behaves anomalously i.e it expands instead of contracting further. So, ice at 0 degrees is less dense than water at 4 degrees.
When a lake starts getting cold, the water at the top hits 4 degrees becomes dense and sinks to the bottom, this keeps happening until all water in the lake has reached 4 deg Celsius. Now, when the temperature outside drops further, and the water at the top falls to 0 degree Celsius, the surface turns to ice. But ice at the top is less dense than the water at the bottom. So, it does not sink. This is why when you see a lake frozen at the top, the water below still remains at an even temperature of 4 degrees, where aquatic life can survive. This is how the anomalous expansion of water plays a major role in the sustenance of aquatic life in cold places.

Answer: Option C. -> Excessive use of groundwater and shortage of rainfall
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C
Groundwater depletion is observed when the groundwater overconsumption is not constantly replenished by water bodies like lakes and flowing rivers or rainfall. Hence, boththe shortage of rainfall and excessive use of groundwater will lead to depletion of water table.

Answer: Option A. -> Uneven distribution of rain.
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A
The uneven distribution of rainwater causes floods in one area while drought in the other. Some places have a good amount of rainfall and are water rich. Other places, like deserts have scanty rainfall.
Excessive rain causes floods in some areas. Parts of Bihar and Uttar Pradesh are hit by floods almost every year during the rainy season. Whereas other places like Rajasthan have scanty rainfall and face drought. We should promote rainwater harvesting in areas which have low rainfall.

Answer: Option B. -> False
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B
Pumping out of water at a rate faster than its rate of replenishment leads to water depletion. Water depletion is more prominent in urban areas where excessive population, industrialisation and urbanisation put a strain on groundwater reserves. Hence, the above statement is incorrect.