Question

Which of the following is not a mixture?
(a) milk and chocolate
(b) sulphur
(c) air
(d) brass

Answer 1

A mixture is a substance which is further composed of two or more different types of components.

Complete answer:
The components in a mixture may or may not be combined chemically to each other.
(a) Milk and chocolate are a mixture. This mixture comprises the components, milk and chocolate as the name suggests.
(b) Sulphur is not a mixture. It is an element with a molecular formula of ${{S}_{8}}$.
Though the molecule of sulphur is made of $8$ atoms of sulphur, it is not a mixture because all the atoms of an element have the same chemical and physical properties. Since it is made of the same kind of atoms, it is therefore not a mixture.
(c) Air is a mixture. It is composed of various types of gases in different amounts.
E.g., It comprises, approximately $78\%$ Nitrogen, $21\%$oxygen and other gases.
(d) Brass is a mixture. It is an alloy of copper and zinc. Usually, brass consists of $66\%$copper and $34\%$ zinc.

Note:
A mixture may or may not have the same composition throughout based on these mixtures are classified as homogeneous and heterogeneous. A homogenous mixture is the one which has the same composition throughout the substance where a heterogenous mixture is where the composition of substance varies throughout the mixture.
The combination of metals to make a new metal is called an alloy. An alloy has properties different from its constituent metals.
Molecules of an element $({{S}_{8}},{{O}_{2}},{{H}_{2\text{ }}}\text{etc}\text{.)}$ are not a mixture, whereas molecule of compound $({{\text{H}}_{2}}O\text{ , C}{{\text{O}}_{2}}\text{ etc}\text{.)}$are a mixture.