Four point charges of magnitudes \( + q\), \( + q\), \( - q\), and \( - q\) are held in place at the corners of a square of side \(r\).

The Coulomb constant is \(k\). Which of the following is the electrical potential at the centre of the square O?

A.     0

B.     \(\frac{{4kq}}{r}\)

C.     \(\frac{{4kq\sqrt 2 }}{r}\)

D.     \(\frac{{ - 4kq\sqrt 2 }}{{{r^2}}}\)

A