Ohm’s law is applicable to –
A) Diode
B) Transistor
C) Electrolyte
D) Conductor

Hint: We need to understand the use of Ohm’s law and its relation with the material under consideration. The Ohm’s law is a direct relation between the potential drop of a resistor and the current flowing through it. We need to compare these for each quantity.

Complete answer:
The Ohm’s law is one of the most basic laws in current electricity. It relates the potential difference of a resistor to the current flowing through it. According to Ohm’s law, the potential difference across a resistor is directly proportional to the current flowing through it. It is mathematically given as –
\[\begin{align}
  & V\propto I \\
 & \Rightarrow V=IR \\
\end{align}\]
Where, V is the potential drop, I is the current and R is the resistance of the resistor.
We know from the equation that the V-I characteristics for a material which obeys Ohm’s law must have a straight-line graph with the slope equal to the resistance as shown below.
        
The above graph shows the V-I characteristics of a \[2\Omega \] resistor.
We know that this characteristic is only observed for Ohmic materials which are conductors.
We can compare the V-I characteristics of a diode, transistor and an electrolyte to prove this.
For diode: The V-I characteristic of diode is given below.
                
For transistor: The below is the output characteristics of a transistor. The input characteristics are similar to the diode characteristics.


The V-I relation in electrolytes is not linear and therefore, doesn’t obey Ohm’s law.
The conductors are the materials which obey the Ohm’s law.

The correct answer is option D.

Note:
The conductors, generally called as resistors, follow Ohm's law to a great-extend. They tend to deviate from the linear condition when the temperature becomes too much higher than normal conditions. Most of the conductors are Ohmic in normal conditions.