Question

When the solute is present in trace quantities the following expressions is used:
A. $0.1M$
B. milligram percent
C. microgram percent
D. parts per million

Answer 1

Every physical quantity is expressed in units. The measurement of any physical quantity has two parts i.e. number and unit.
Example: Weight of an object is 45kg, then it has two parts, number 45 and unit kg.

Complete step by step answer:
There are seven basic physical quantities-

Physical quantity	Unit in SI system
Length$(l)$	Meter$(m)$
Mass$(m)$	Kilogram$(kg)$
Time$(t)$	Second$(s)$
Electric current$(I)$	Ampere$(A)$
Thermodynamic temperature$(T)$	Kelvin$(K)$
Amount of substance$(n)$	Mole$(mol)$
Luminous intensity${I_v}$	Candela$(Cd)$

The unit of mass is in kilogram. But the term “weight” should be used in place of “mass”. Both have different meanings.
Mass is the quantity of matter contained in a sample. It is constant.
Weight is force with which the body is attracted towards the earth due to earth’s gravity, $g$. Gravity of the earth changes with height.
Unit of mass is $kg$ in S.I. system of units and$gram$in C.G.S. system of units.
S.I. units and C.G.S units are used when a large amount of substance is expressed in terms of their concentration.
But when substance present in trace, it is represented by parts per million (ppm)
Part-per notation is a set of pseudo-units that describe small values of different dimensions’ qualities.
Mass in ppm represented as milligram per liter.
Generally contamination is measured in $ppm.$
The range of drinking water is $30$ to 400$$$$ppm, it means water should contain impurities between $30mg$ to $400mg$ in $1000ml$

So, the correct answer is “Option D”.

Note:
To find concentration in$ppm,$ The equation, mass solute (mg)/Volume (L) is used.
If mass of solute$NaCl$ is $0.0045gm.$
On converting it into mg $= 4.5mg.$
We can convert it into percentage also if $20ppm$ is given, it is equal to $0.002\%$ and $40ppm$ is equal to $0.004\%$