Final answer:
The potential at the empty corner of a square with two positive and one negative point charge is the algebraic sum of the individual potentials and could be either positive or negative, depending on the exact values and positions of the charges.
Step-by-step explanation:
The student's question asks about the electric potential at the empty corner of a square when three point charges with identical magnitudes are placed at the other corners, with two being positive and one being negative. In any arrangement of these three charges on a square, the electric potential at the empty corner is always the algebraic sum of the potentials due to each of the three charges. Since electric potential is a scalar quantity, it is not dependent on the direction of the charges, only their magnitude and sign.
The potential due to a positive charge is positive, while the potential due to a negative charge is negative. When you have two positive charges and one negative charge, the total potential is calculated by adding two positive potentials due to the positive charges and one negative potential due to the negative charge. Therefore, depending on the exact magnitudes of the charges and their distances from the empty corner, the sign of the total potential could be either positive or negative, but it won't be zero unless the magnitudes of the charges are specifically arranged to cancel each other out, which was not specified in the scenario.