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# In which year the SI system of units was developed and recommended by the general conference on weights and measures?A) $1951$B) $1961$C) $1971$D) $1981$

Last updated date: 13th Jun 2024
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Hint:SI unit is an abbreviation of the French word System International. The International System of Units (SI) is the metric system that is universally accepted as a standard for measurements.

Complete step by step solution:
The SI system of units was developed and recommended by the General Conference on Weights and Measures in$1971$.
SI units have an important contribution in scientific and technological research and development. It comprises $7$ base units which are used for defining $22$ derived units.
The basic $7$ fundamental units for fundamental quantities are as following,
Physical Quantities
S.I. Unit
For Mass is Kilogram ($kg$)
For Length is Meter ($m$)
For Time is Second ($s$)
For Electric current is Ampere ($A$)
For Temperature is Kelvin ($K$)
For Amount of substance is Mole ($mol$)
For Luminous intensity is Candela ($cd$)

Unit of length, meter ($m$): Meter is the SI unit of length and is defined by taking the fixed value of the speed of light in vacuum. It is expressed as $m{{s}^{-1}}$.

Unit of mass, kilogram ($kg$): Kilogram is the SI unit of mass and is defined by taking the fixed value of the Planck constant. It is expressed as $kg{{m}^{2}}.{{s}^{-1}}$.

Unit of time, second ($s$): Second is the SI unit of time and is defined by taking the fixed value of Cesium frequency. It is expressed as ${{s}^{1}}$.

Unit of electric current, ampere ($A$): Ampere is the SI unit of electric current and is defined by taking the fixed value of the elementary charge.

Unit of thermodynamic temperature, Kelvin ($K$): Kelvin is the SI unit of thermodynamic temperature and is defined by taking the fixed value of Boltzmann constant $k=1.380649\times {{10}^{-23}}$.

Unit of the amount of substance, mole ($mol$): Mole is the SI unit of amount of substance and is defined by the fixed value of Avogadro constant ${{N}_{A}}$. One mole contains $6.02214076\times {{10}^{23}}$ elementary entities and is expressed as $mo{{l}^{-1}}$.

Unit of luminous intensity, candela ($cd$): Candela is the SI unit of luminous intensity and is defined by the fixed value of the luminous efficacy.

Note: The fundamental units are independent of any other units including themselves.
There are a total of seven fundamental units in the SI unit system.
The derived units are those units which are obtained by mathematical operations of fundamental units.