Question

Alloying is not done for which of the following purpose?

• A. To enhance the hardness of the metal
• B. To enhance the tensile strength
• C. To modify colour
• D. To raise the melting point

Answer 1

The correct option is D

To raise the melting point

Alloy: The homogeneous mixture of two or more metals or non-metals to improve their various properties of them, is called an alloy.

For example, aluminium $\left(\mathrm{Al}\right)$ is light but not strong, but an alloy of aluminium with copper $\left(\mathrm{Cu}\right)$, magnesium $\left(\mathrm{Mg}\right)$ and manganese $\left(\mathrm{Mn}\right)$ called duralumin is light as well as strong. It is used for making aircraft bodies and parts, space satellites and kitchenware.

More examples are: Brass is an alloy of copper $\left(\mathrm{Cu}\right)$ and zinc $\left(\mathrm{Zn}\right)$, Bronze is an alloy of copper $\left(\mathrm{Cu}\right)$ and tin $\left(\mathrm{Sn}\right)$, etc.

The explanation for the correct option:

Alloying is not done to raise the melting point. Alloys have lower melting points than constituent metals. The different sizes of atoms in an alloy make their arrangement less regular than a pure metal. This makes the bonds between the atoms weaker and lowers the melting point.

The explanation for incorrect options:

The properties of an alloy are different from the properties of the constituent metals:

1. Alloys are stronger than the metals from which they are made.
2. Alloys are harder than their constituent metals.
3. Alloys are more resistant to corrosion.
4. Alloys have lower melting points than constituent metals.
5. Alloys have lower electrical conductivity than pure metals.

Therefore, Options (A), (B) and (C) are incorrect as alloying is done for these purposes.

Therefore, the correct option is (D).