In an electrical wire copper is used for electrical conduction mainly because:
A) It has a high melting point.
B) It is cheaper.
C) It is very durable.
D) It has low electrical resistivity.

Hint: An electric current consists of charges in motion from one region to another. When this motion takes place within a conducting path that forms a closed loop, called an electric circuit. And those conducting path or conducting substance use to complete this path is called electrical wire. The conductivity of an electrical wire is inversely proportional to the resistance offered.

Complete step by step answer:
Copper is a good conductor of electricity. It allows the electric current to pass through it easily. In conductors or metals, there are large numbers of free electrons. When an electric field is applied to the conductor or copper the free electrons start drifting in a particular direction opposite to the applied electric field to constitute an electric current.
Resistance is an opposition offered by the substance to the flow of electric current. This opposition occurs because atoms or molecules of the substance obstruct the flow of charge that is here free electrons in copper. In the case of copper, there is very little opposition to the flow of electric current.
Metals or conductors have low resistivity in the range of $10^{-8}$ to $10^{-6}$ Ohm-meters.

The remaining options also hold good for copper. But the main and very important reason for using copper in the electrical wire is its low electrical resistivity.
As we all know gold is also a very good conductor of electricity. But which is much costlier than copper. Similarly, silver is also a good conductor of electricity, it has low resistivity. But again, silver is also more expensive than copper. Therefore, we cannot use silver and gold. And also, copper has a high melting point and durable substance.
From all these discussions we can say that in an electrical wire copper is used for electrical conduction mainly because it has low electrical resistivity.

Therefore, the correct option is D.

Note:
The resistivity of a material is the resistance offered by the one-meter length of conductor of the materials having an area of a cross-section of A.
The resistivity of a material depends on the nature of the material of the conductor used, temperature.