Charges are placed on the vertices of a square as shown. Let E be the electric field and V the potential at the centre. If the charges on A and B are interchanged with those on D and C respectively. Then which of the E or V will change or remains unchanged?

Given that, the charges are placed on the vertices of the square.



Let, the distance from the centre of the square to the vertex be 'a'.
Potential before and after interchanging the charges is 0 .
Direction of electric field before and after interchainging the charges is shown below. we can see that, after interchanging the charges A and B with C and D, the direction of electric field has reversed.
Therefore, electric field changes and potential remains constant.