The example of non-ohmic conductor is:
A.)Copper wire
B.)Aluminum wire
C.)Diode
D.)Silver wire

Hint: To follow ohmic conductor property, the graph of V v/s I of that particular material must have passed through origin and must be straight. Graphs of copper wire, aluminum wire and silver wire do possess this property. Graphs of diodes are not straight and do not pass through origin.

Complete step by step solution:
The relationship between current through a conductor and applied potential difference was first discovered by German scientists George simon for home in 1828. This relationship is known as Ohm's law.
As long as a physical state (material, dimensions and temperature) of a conductor remains the same, the electric current flowing through a given conductor is directly proportional to the potential difference applied across it.

$\begin{align}
  & I\alpha V \\
 & I=\dfrac{V}{R} \\
 & V=IR \\
\end{align}$
$R=\dfrac{V}{I}$-----(1)

Equation one is valid only when the graph of resistance will be straight line.
Where they are in constant proportion. It represents the opposition to flow of current and is known as reduced and the graph of current versus potential difference across a conductor is straight line.





So
All the examples given in options follow ohmic law except Diode.
Diode follows a non-ohmic conductor whose graph is not a straight line.
In general resistance is given by the rate ratio of applied potential across the conductor to the resulting current through it.