Two thin wire rings each having radius R are placed at distance d apart with their axes coinciding. The charges on the two are `+Q` and `-Q`. The potential difference between the centre so the two rings is

Options

A. zero
B. `(Q)/(4pi epsilon_(0)) [(1)/(4)-(1)/(sqrt(R^(2)+d^(2)))]`
C. `(Q)/(4pi epsilon_(0)d^(2)) `
D. `(Q)/(2pi epsilon_(0)) [(1)/(R)-(1)/(sqrt(R^(2)+d^(2)))]`