Introduction
When an external electric potential difference is applied across a conductor, the electrons flow in the opposite direction to the current. This phenomenon is known as the flow of electric current.

Explanation
The number of free electrons in the conductor does not decrease when an external electric potential difference is applied across the conductor. This is because the electrons are already present in the conductor and are free to move about.

When an external electric potential difference is applied across the conductor, the electrons are induced to move in the opposite direction of the current. This is because the electric field produced by the potential difference exerts a force on the electrons, causing them to move in the opposite direction of the current.

The number of free electrons in the conductor remains the same because the electric field produced by the potential difference does not create or destroy any electrons. It simply causes the existing electrons to move in a particular direction.

Conclusion
In conclusion, the number of free electrons in a conductor does not decrease when an external electric potential difference is applied across the conductor. The electrons are induced to move in the opposite direction of the current, but the number of free electrons in the conductor remains the same. This phenomenon is the result of the electric field produced by the potential difference, which exerts a force on the electrons, causing them to move in the opposite direction of the current.

Once a potential is applied to a conductor, a constant potential difference is maintained across the two ends of the capacitor. One end will have a constant positive potential and the other end will have a constant negative potential. And also, since a complete path is available for the electron, the electrons exiting from the positive terminal of the conductor will travel through the circuit and enter again from the end maintained at negative end. Hence the electrons in the conductor do not exhaust.