Two large vertical and parallel metal plates having a separation of...

Two large vertical and parallel metal plates having a separation of \( 1 \mathrm{~cm} \) are connected to a DC voltage source of potential difference \( X \). A proton is released at rest midway between the two plates. It is found to move at \( 45^{\circ} \) to the vertical just before touching the plate having lower potential. Then, \( X \) is nearly
(a) \( 10^{5} \mathrm{~V} \)
(b) \( 10^{7} \mathrm{~V} \)
(c) \( 10^{9} \mathrm{~V} \)
(d) None of these