Which one of the following is considered to be the purest source of water?
- A.River water
- B.Sea water
- C.Well water
- D.Rain water
Correct answer
Explanation
The correct answer is D, Rain water. Rain water is the purest natural form of water because it is formed by evaporation and condensation, a natural distillation. When the Sun heats seas, rivers and lakes, only water evaporates; the dissolved salts, minerals and most impurities are left behind. The vapour then cools and condenses into clouds and falls as rain. That is why rain water is nearly free of dissolved salts and is soft. It can, however, pick up some dust and gases such as carbon dioxide, and near polluted areas sulphur and nitrogen oxides, which is how acid rain forms. Option A is wrong because river water carries dissolved salts, silt and organic matter collected along its course. Option B is wrong because sea water is the most impure, holding about 3.5 per cent dissolved salts. Option C is wrong because well water dissolves minerals such as calcium and magnesium salts from rocks underground and is often hard. Exam tip: rain water is nature's distilled water; sea water is the least pure.
Practice Questions
View allWhich one of the following plant tissues has dead cells ?
- A.Epidermis
- B.Parenchyma
- C.Collenchyma
- D.Sclerenchyma
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Sclerenchyma cells are dead at maturity, with thick walls hardened by lignin. Sclerenchyma is the tissue that makes plants hard and stiff.
Read the full explanation →Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by
- A.the Right-Hand Thumb rule and it would be in the downward direction.
- B.the Left-Hand Thumb rule and it would be in the downward direction.
- C.the Right-Hand Thumb rule and it would be in the upward direction.
- D.the Left-Hand Thumb rule and it would be in the upward direction.
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For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.
Read the full explanation →Which one of the following statements is true for sound waves propagating in air?
- A.Sound is an electromagnetic wave and transverse in nature
- B.Sound is a mechanical wave and longitudinal in nature
- C.Sound is a mechanical wave and transverse in nature
- D.Sound is an electromagnetic wave and longitudinal in nature
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Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.
Read the full explanation →Which one of the following is primarily responsible for conduction of current in a metal?
- A.Bound electrons
- B.Free electrons
- C.Both bound and free electrons
- D.Ions
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In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.
Read the full explanation →Which one of the following statements is correct about the magnification of an optical microscope?
- A.Magnification increases with the increase in focal length of eyepiece
- B.Magnification increases with the increase in focal length of objective
- C.Magnification does not depend upon the focal length of eyepiece
- D.Magnification decreases with the increase in focal length of eyepiece
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A compound microscope magnifies more when both its lenses have short focal lengths. In a compound microscope the objective forms a real, enlarged image, and the eyepiece magnifies it further like a simple magnifier.
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