What is the chemical formula for water?
a) H2​O
b) H2​O2​
c) HO2​
d) H2​O3​
Answer: a) H2​O

Which of the following is the most common solvent in the world?
a) Alcohol
b) Oil
c) Water
d) Acetone
Answer: c) Water

What is the process called when water changes from a liquid to a gas?
a) Condensation
b) Evaporation
c) Sublimation
d) Precipitation
Answer: b) Evaporation

Which gas is most commonly dissolved in water?
a) Oxygen
b) Carbon dioxide
c) Nitrogen
d) Hydrogen
Answer: a) Oxygen

What is the primary source of freshwater on Earth?
a) Oceans
b) Lakes
c) Rivers
d) Glaciers
Answer: d) Glaciers

The process by which water is purified naturally as it moves through the soil is called:
a) Filtration
b) Sedimentation
c) Percolation
d) Distillation
Answer: c) Percolation

Hard water is water that contains a high concentration of:
a) Sodium ions
b) Magnesium and calcium ions
c) Potassium ions
d) Hydrogen ions
Answer: b) Magnesium and calcium ions

What is the unit used to measure water hardness?
a) Grams per liter
b) Parts per million (ppm)
c) Milligrams per liter
d) Liters per second
Answer: b) Parts per million (ppm)

Which method is used to remove hardness from water?
a) Filtration
b) Distillation
c) Ion exchange
d) Boiling
Answer: c) Ion exchange

What type of pollution is caused by the addition of excessive nutrients to water bodies?
a) Thermal pollution
b) Eutrophication
c) Acidification
d) Salinization
Answer: b) Eutrophication

The pH of pure water is:
a) 5
b) 7
c) 9
d) 11
Answer: b) 7