Which one among the following metals is not stored under oil ?
- A.Sodium
- B.Rubidium
- C.Potassium
- D.Lithium
Correct answer
Explanation
The correct answer is D, Lithium. Lithium is so light that it floats on kerosene or paraffin oil, so it is kept coated in petroleum jelly or paraffin wax, or under an inert gas, instead of under oil.
The alkali metals react quickly with oxygen and moisture in the air, and sodium and potassium even catch fire in water. To keep air away from them they are stored under kerosene or paraffin oil. Lithium's density is only about 0.53 g per cubic centimetre, the lowest of all metals and less than that of these oils, so a piece of lithium rises to the surface and is exposed to air. That is why it is sealed in wax or jelly instead.
A is wrong: sodium is the classic example of a metal kept under kerosene.
B is wrong: rubidium is heavier than oil and is stored under oil or in sealed ampoules.
C is wrong: potassium sinks in kerosene and is stored under it.
Exam tip: sodium and potassium go under kerosene, white phosphorus under water, and lithium in petroleum jelly or wax because it floats on oil.
Practice Questions
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- B.Thomas Newcomen
- C.James Watt
- D.Richard Arkwright
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- B.10 Ω
- C.5 Ω
- D.15 Ω
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- B.nearby object is focused before the retina.
- C.distant object is focused before the retina.
- D.distant object is focused beyond the retina.
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- B.nose
- C.ear
- D.urinary bladder
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