The mole is the SI base unit of which quantity?
- A.Mass
- B.Amount of substance
- C.Density
- D.Volume
Correct answer
Explanation
The correct answer is B, amount of substance. The mole is the chemist's counting unit: one mole of any substance contains the Avogadro number of particles, about six followed by twenty-three zeros, whether those particles are atoms, molecules or ions. It is one of the seven base units of the SI system and is written with the symbol mol.
Option A, mass, has the kilogram as its base unit; the two are related through molar mass but are not the same quantity. Option C, density, is a derived quantity measured in kilograms per cubic metre. Option D, volume, is also derived and is measured in cubic metres, with the litre used as a convenient practical unit. Questions of this type test the pairing of each base unit with its own quantity, so learn all seven pairs together.
Read the full article: Units and Measurements: SI Units, Dimensions and Instruments
Practice Questions
View allWhat is the SI unit of force?
- A.Joule
- B.Newton
- C.Watt
- D.Pascal
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One newton is the force that gives a mass of one kilogram an acceleration of one metre per second squared, which follows directly from the equation force equals mass times acceleration.
Read the full explanation →How many base units are there in the International System of Units (SI)?
- A.Five
- B.Six
- C.Seven
- D.Nine
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The SI system, adopted in 1960 by the General Conference on Weights and Measures, rests on seven base units: the metre, the kilogram, the second, the ampere, the kelvin, the mole and the candela.
Read the full explanation →Which one of the following is NOT a base unit of the SI system?
- A.Kelvin
- B.Mole
- C.Newton
- D.Candela
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The newton is a derived unit: it is built from the kilogram, the metre and the second, since force equals mass times acceleration, and it can be written as one kilogram metre per second squared.
Read the full explanation →The candela is the SI unit of which physical quantity?
- A.Luminous intensity
- B.Electric current
- C.Amount of substance
- D.Pressure
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The candela takes its name from the candle, which was once used as a rough standard of light, and it is one of the seven base units of the SI system.
Read the full explanation →A light year is a unit of which of the following?
- A.Time
- B.Distance
- C.Speed
- D.Brightness of a star
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A light year is the distance that light, moving at about three lakh kilometres per second, covers in one year, which works out to roughly 9.46 trillion kilometres.
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