The student is asking about the position on the x-axis where the total electric field due to a nucleus with 18 protons is zero. This involves the use of electromagnetism principles and requires considering any other charges present that could cancel the field created by the nucleus.
The question is concerning the principle of electric fields and their cancellation, which can be answered using concepts from classical electromagnetism. A nucleus with 18 protons will create a positive electric field that radiates outward from its position on the x-axis. To find the position where the total electric field is zero, one would need to set up an equation that considers both the electric field produced by this nucleus and the electric fields generated by any other charges present in the system, ensuring that the vector sum of these electric fields equals zero.
In the scenario depicted, since no other charges are described, we might be missing information about additional charges that would be required to create an opposing electric field (assuming we are not considering the fields at infinity). However, more commonly, a charge or charges would be placed at various points on the axis, and the points at which the total electric field cancels out would be determined by using Coulomb's law and the principle of superposition.