Question

Which of the following are impure substances?
A.Elements
B.Compounds
C.Mixtures
D.None of these

Answer 1

Hint: An impure substance is made of two or more elements or compounds that are not bonded together chemically.

Complete step by step answer:
For a substance to be impure, it should have following characteristics:
-It is made up of two or more pure substances mixed together in any proportion.
-It is formed when there is a physical change.
-They have a variable composition.
-An element consists of only one atom. An element cannot be broken down or transformed into a new substance even by using some physical or chemical means, thus it is a pure substance.
Examples of Elements are metals, nonmetals and metalloids.
-A compound is formed when two or more elements are combined chemically in a fixed ratio. A compound can’t be broken down into more than one kind of its substance by using physical or chemical means. This makes a compound a pure substance.
Examples of compounds are water, carbon dioxide, common salt etc.
-A mixture is made of different molecules/atoms which are combined together physically in an unknown ratio. A mixture can be easily separated by physical process. Hence, this makes mixture an impure substance.
Examples of mixtures are air, petroleum, a solution of sugar in water are mixtures.

Hence option C is correct.

Note:
Compounds are also mixtures of different substances but are pure substances because they are in a fixed ratio whereas Impure substances are mixtures of different substances in different ratios.