Question

The standard quantity used for comparison is called
(A) Scale
(B) Unit
(C) Magnitude
(D) All

Answer 1

Hint Every physical quantity needs a standard for its specification which is required for identification, comparisons and for expressing other physical quantities as well. All the comparisons with physical quantities are made in terms of units.

Complete step-by-step solution
Measuring a physical quantity includes comparison with certain basic internationally approved reference standards called units. A physical quantities measurement is written in terms of the standard unit with the numerical value. Each unit has its symbol.
For example:


From the diagram, the radius of the circle is 5 cm.
The diameter of the circle is 10 cm. Here cm is the standard unit giving meaning to the numerical value 5 and 10.

There are many systems of units like S.I, CGS, FPS, MKS and more but the S.I units system is the standard scheme for international usage in scientific work. The S.I system has seven base/fundamental units from which other units are derived called secondary derived units. Using these base units the dimensional formulae of physical quantities are also derived.

Quantity	Unit	Symbol
Length	Meter	m
Mass	Kilogram	Kg
Time	Second	S
Temperature	Kelvin	K
Amount of substance	Mole	Mol
Electric current	Ampere	A
Luminous intensity	Candela	Cd

Besides the above seven fundamental units two supplementary units exist.

Quantity	Unit	Symbols
Plane angle	Radian	Rad
Solid angle	Steradian	Sr

So, B is the correct option.

Note: The units of other physical quantities are derived from the base units.
For example: Unit of length is m and unit of time is s from this unit of velocity \[m{s^{ - 1}}\] is derived. The units can be converted from one to other forms of the same physical quantity like kg, g, mg, dg all are the units for measuring mass.