Water

1. Water is a:
   a) Element
   b) Compound
   c) Mixture
   d) Isotope
   ✅ b) Compound
   Explanation: Water (H₂O) is a compound made of hydrogen and oxygen.
   (BPSC 64th Prelims)

2. The chemical formula of water is:
   a) H₂O₂
   b) OH
   c) HO₂
   d) H₂O
   ✅ d) H₂O
   Explanation: Water contains two hydrogen atoms and one oxygen atom.
   (BPSC 2021)

3. Which property makes water a universal solvent?
   a) Low boiling point
   b) Polar nature
   c) High density
   d) Inertness
   ✅ b) Polar nature
   Explanation: Water’s polarity allows it to dissolve many ionic and polar substances.
   (BPSC CDPO 2019)

4. The pH value of pure water at 25°C is:
   a) 9
   b) 0
   c) 7
   d) 14
   ✅ c) 7
   Explanation: Pure water is neutral, having a pH of 7.
   (BPSC Assistant 2017)

5. Which of the following diseases is caused by drinking contaminated water?
   a) Malaria
   b) Typhoid
   c) Dengue
   d) Tuberculosis
   ✅ b) Typhoid
   Explanation: Typhoid is a water-borne disease caused by Salmonella typhi.
   (BPSC 66th)

6. Which process is used for removing salts from seawater?
   a) Filtration
   b) Sedimentation
   c) Distillation
   d) Chlorination
   ✅ c) Distillation
   Explanation: Desalination through distillation removes salt from seawater.
   (BPSC 65th)

7. Which river is known as the lifeline of Bihar?
   a) Ganga
   b) Kosi
   c) Sone
   d) Gandak
   ✅ a) Ganga
   Explanation: The Ganga provides irrigation, drinking water, and sustains livelihoods.
   (BPSC Teacher 2023)

8. Which gas is dissolved in water to support aquatic life?
   a) Nitrogen
   b) Hydrogen
   c) Oxygen
   d) Carbon dioxide
   ✅ c) Oxygen
   Explanation: Dissolved oxygen is necessary for aquatic organisms to survive.
   (BPSC 67th Prelims)

9. Water boils at what temperature under normal pressure?
   a) 80°C
   b) 100°C
   c) 110°C
   d) 120°C
   ✅ b) 100°C
   Explanation: Boiling point of pure water at 1 atm pressure is 100°C.
   (BPSC 2018)

10. What is the primary cause of water hardness?
    a) Sodium chloride
    b) Calcium and magnesium salts
    c) Iron oxide
    d) Sulphur
    ✅ b) Calcium and magnesium salts
    Explanation: Temporary and permanent hardness arise due to calcium and magnesium ions.
    (BPSC 66th)

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NCERT-Based MCQs (Q11–30)

1. Which of the following is a physical property of water?
   a) Combustibility
   b) Solubility
   c) Radioactivity
   d) Magnetic nature
   ✅ b) Solubility
   Explanation: Water dissolves more substances than any other liquid.

2. What is the state of water at 0°C under normal pressure?
   a) Solid only
   b) Liquid only
   c) Both solid and liquid
   d) Gas
   ✅ c) Both solid and liquid
   Explanation: At 0°C, water exists in equilibrium between ice and liquid.

3. Which process in nature uses water to form clouds?
   a) Condensation
   b) Precipitation
   c) Sublimation
   d) Evaporation
   ✅ a) Condensation
   Explanation: Water vapor cools and condenses into clouds.

4. Water vapor in the atmosphere is an example of:
   a) Solid
   b) Liquid
   c) Gas
   d) Plasma
   ✅ c) Gas
   Explanation: Water vapor is water in gaseous state.

5. Which bond is responsible for the high boiling point of water?
   a) Covalent
   b) Ionic
   c) Hydrogen bond
   d) Metallic
   ✅ c) Hydrogen bond
   Explanation: Hydrogen bonding between H₂O molecules increases boiling point.

6. What is the density of water at 4°C?
   a) 0.8 g/cm³
   b) 1.0 g/cm³
   c) 1.2 g/cm³
   d) 0.6 g/cm³
   ✅ b) 1.0 g/cm³
   Explanation: Water has maximum density at 4°C.

7. Water expands when:
   a) Heated
   b) Cooled below 4°C
   c) Frozen
   d) Both b and c
   ✅ d) Both b and c
   Explanation: Water shows anomalous expansion below 4°C and during freezing.

8. Water is essential for:
   a) Transport of nutrients
   b) Digestion
   c) Temperature regulation
   d) All of the above
   ✅ d) All of the above
   Explanation: Water plays key roles in biological functions.

9. Which part of the water cycle involves infiltration?
   a) Precipitation
   b) Evaporation
   c) Groundwater recharge
   d) Condensation
   ✅ c) Groundwater recharge
   Explanation: Infiltration is when water seeps into the soil to recharge aquifers.

10. Which water treatment step kills pathogens?
    a) Filtration
    b) Sedimentation
    c) Chlorination
    d) Decantation
    ✅ c) Chlorination
    Explanation: Chlorine disinfects water and kills microbes.

11. What is the chemical nature of water?
    a) Acidic
    b) Basic
    c) Neutral
    d) Depends on container
    ✅ c) Neutral
    Explanation: Pure water is neither acidic nor basic.

12. What percent of Earth's surface is covered by water?
    a) 51%
    b) 61%
    c) 71%
    d) 81%
    ✅ c) 71%
    Explanation: Oceans cover the majority of the Earth’s surface.

13. What is potable water?
    a) Water used in agriculture
    b) Water in oceans
    c) Water fit for drinking
    d) Distilled water only
    ✅ c) Water fit for drinking
    Explanation: Potable water is clean and safe for human consumption.

14. Which organ regulates water in the human body?
    a) Liver
    b) Kidney
    c) Heart
    d) Lungs
    ✅ b) Kidney
    Explanation: Kidneys filter blood and maintain water balance.

15. Hard water does not form lather with:
    a) Soap
    b) Detergent
    c) Shampoo
    d) None
    ✅ a) Soap
    Explanation: Soap reacts with calcium/magnesium forming scum in hard water.

16. Boiling of water is a:
    a) Physical change
    b) Chemical change
    c) Nuclear change
    d) Irreversible change
    ✅ a) Physical change
    Explanation: No new substance is formed during boiling.

17. Ice floats on water because:
    a) It is heavier
    b) It has higher density
    c) It has lower density
    d) It absorbs water
    ✅ c) It has lower density
    Explanation: Ice expands and becomes less dense than liquid water.

18. Which one is a hydrological process?
    a) Erosion
    b) Precipitation
    c) Earthquake
    d) Sedimentation
    ✅ b) Precipitation
    Explanation: Rainfall and snowfall are forms of precipitation in the water cycle.

19. The boiling point of water changes with:
    a) Volume
    b) Pressure
    c) Stirring
    d) Container type
    ✅ b) Pressure
    Explanation: Boiling point increases with higher pressure and decreases at lower pressure.

20. Which of the following contains the least amount of fresh water?
    a) Rivers
    b) Lakes
    c) Glaciers
    d) Oceans
    ✅ d) Oceans
    Explanation: Oceans are saltwater; freshwater sources are rivers, lakes, and glaciers.

21. Which of the following techniques is used to purify water in villages?
    a) Filtration through paper
    b) UV sterilization
    c) Boiling
    d) Ion exchange
    ✅ c) Boiling
    Explanation: Boiling is the most common and cost-effective way to kill microbes in water.

22. Which gas is released when water reacts with sodium?
    a) Oxygen
    b) Nitrogen
    c) Hydrogen
    d) Methane
    ✅ c) Hydrogen
    Explanation: Sodium reacts vigorously with water to form sodium hydroxide and hydrogen gas.

23. Which of the following is NOT a use of water in industries?
    a) Cooling
    b) Washing
    c) Solvent in chemical processes
    d) Conduction of electricity
    ✅ d) Conduction of electricity
    Explanation: Pure water is a poor conductor of electricity.

24. Which of these is a biological method of water purification?
    a) Reverse osmosis
    b) Chlorination
    c) Slow sand filtration
    d) Distillation
    ✅ c) Slow sand filtration
    Explanation: It uses biological layers to remove pathogens and particles.

25. What is the role of alum in water purification?
    a) Disinfection
    b) Coagulation
    c) Filtration
    d) Desalination
    ✅ b) Coagulation
    Explanation: Alum helps clump suspended impurities for easier removal.

26. What is the major component of rainwater harvesting?
    a) Chlorination
    b) Runoff canal
    c) Catchment and storage system
    d) Borewell recharge
    ✅ c) Catchment and storage system
    Explanation: Rainwater is collected from rooftops and stored for reuse.

27. Which layer of the Earth contains the most groundwater?
    a) Crust
    b) Mantle
    c) Aquifer
    d) Core
    ✅ c) Aquifer
    Explanation: Aquifers are underground layers storing water.

28. Which property of water helps in maintaining temperature in the body?
    a) Low boiling point
    b) High specific heat
    c) High density
    d) High surface tension
    ✅ b) High specific heat
    Explanation: It helps regulate body temperature by absorbing more heat without rapid warming.

29. Which water source is most prone to fluoride contamination in Bihar?
    a) Ponds
    b) Wells
    c) Rivers
    d) Rainwater
    ✅ b) Wells
    Explanation: Deep groundwater sources in some Bihar districts show fluoride contamination.

30. The ability of water to move upwards in plants is due to:
    a) Osmosis
    b) Diffusion
    c) Capillary action
    d) Evaporation
    ✅ c) Capillary action
    Explanation: Water moves against gravity in small xylem vessels due to cohesion and adhesion.

31. What is the term for water below the Earth's surface?
    a) Rainwater
    b) Stream water
    c) Groundwater
    d) Freshwater
    ✅ c) Groundwater
    Explanation: Groundwater is stored in aquifers below the Earth’s surface.

32. Which of the following is a water pollutant?
    a) Oxygen
    b) Carbon dioxide
    c) Lead
    d) Hydrogen
    ✅ c) Lead
    Explanation: Lead from pipes and industrial waste pollutes water.

33. What is responsible for temporary hardness of water?
    a) Magnesium sulfate
    b) Calcium chloride
    c) Calcium bicarbonate
    d) Sodium nitrate
    ✅ c) Calcium bicarbonate
    Explanation: Temporary hardness is caused by bicarbonates which can be removed by boiling.

34. Which of the following does NOT cause water pollution?
    a) Fertilizers
    b) Oil spills
    c) Algae
    d) Untreated sewage
    ✅ c) Algae
    Explanation: Algae can bloom due to pollution but aren't a primary cause.

35. Which of these is a chemical method of water disinfection?
    a) Filtration
    b) Boiling
    c) UV radiation
    d) Chlorination
    ✅ d) Chlorination
    Explanation: Chlorine kills bacteria and viruses chemically.

36. The ocean water is saline due to:
    a) Presence of gases
    b) High temperature
    c) Dissolved salts
    d) High evaporation
    ✅ c) Dissolved salts
    Explanation: Ocean water contains large amounts of dissolved sodium chloride and other salts.

37. The process of converting water vapor into liquid is called:
    a) Evaporation
    b) Condensation
    c) Sublimation
    d) Melting
    ✅ b) Condensation
    Explanation: It's the reverse of evaporation and forms dew or clouds.

38. Water conservation is important because:
    a) It increases pollution
    b) Water is unlimited
    c) Only 1% of Earth’s water is drinkable
    d) Rainfall is regular
    ✅ c) Only 1% of Earth’s water is drinkable
    Explanation: Majority of Earth's water is saltwater or frozen.

39. Which part of India receives the least rainfall?
    a) Cherrapunji
    b) Western Rajasthan
    c) Bihar
    d) Kerala
    ✅ b) Western Rajasthan
    Explanation: Rajasthan is a desert region and gets the least rain.

40. What percent of the human body is water?
    a) 25%
    b) 50%
    c) 70%
    d) 90%
    ✅ c) 70%
    Explanation: Human bodies are composed of about 60–70% water depending on age and sex.