Which of the following is a water-borne disease?
- A.Malaria
- B.Dengue
- C.Cholera
- D.Tuberculosis
Correct answer
Explanation
The correct answer is C, cholera. Cholera is caused by the bacterium Vibrio cholerae and spreads through water and food contaminated with faecal matter, which is why it breaks out after floods and wherever sewage mixes with the water supply; typhoid, hepatitis A, dysentery and polio spread the same way. Options A and B are wrong because malaria and dengue are vector-borne: they are carried by mosquitoes, malaria by the female Anopheles and dengue by Aedes aegypti, and stagnant water matters only as a breeding place for the insect, not as the medium of infection. Option D is wrong because tuberculosis is an airborne disease, spread by droplets from the cough of an infected person. Boiling, chlorination and filtration are the defences against water-borne disease.
Read the full article: Chemistry of Water: Hard Water, Heavy Water, Purification
Practice Questions
View allZero hardness of water is achieved by
- A.using lime soda process
- B.excess lime treatment
- C.ion exchange method
- D.using excess alum dosage
Show answer
In an ion exchange plant the water passes through a cation resin, which takes up the calcium and magnesium ions, and then through an anion resin, which takes up the sulphate, chloride and bicarbonate ions; because the hardness-causing ions are actually taken out of the water, the hardness can be…
Read the full explanation →Heavy water is chemically known as:
- A.Hydrogen peroxide
- B.Deuterium oxide
- C.Tritium oxide
- D.Distilled water
Show answer
Heavy water is D2O, in which both hydrogen atoms are deuterium, the isotope whose nucleus has one proton and one neutron, so its molecular mass is twenty instead of eighteen.
Read the full explanation →The temporary hardness of water is caused by the presence of:
- A.Sulphates of calcium and magnesium
- B.Chlorides of calcium and magnesium
- C.Bicarbonates of calcium and magnesium
- D.Sodium and potassium salts
Show answer
These bicarbonates are formed when water containing dissolved carbon dioxide passes over limestone, and they are unstable; on boiling they lose carbon dioxide and settle as insoluble carbonates, which is why this kind of hardness is called temporary and can be removed by boiling alone, or by the Clark method…
Read the full explanation →Water has its maximum density at which temperature?
- A.0 degree Celsius
- B.4 degree Celsius
- C.25 degree Celsius
- D.100 degree Celsius
Show answer
Water contracts as it is cooled to four degrees, is densest at that temperature, and then expands again as it cools further to zero, which is called the anomalous expansion of water.
Read the full explanation →Alum is added at a water works mainly to:
- A.Kill bacteria and viruses
- B.Coagulate fine suspended particles so that they settle
- C.Remove the permanent hardness of the water
- D.Add fluoride to the water
Show answer
Alum, that is aluminium sulphate or potash alum, is a coagulant: in water it forms a gelatinous hydroxide that gathers the fine clay and colloidal particles into heavier flocs, which then settle in the sedimentation tank and are removed, leaving clear water for filtration.
Read the full explanation →