We know that
F = k * q1 * q2 / d^2
Force of attraction F
K = 8.99 x 10^9
q1 = charge on Mg = +2 = 2 X 1.9 x 10^-19 C
q2 = charge on O = -2 = 2 X 1.9 x 10^-19 C
d = distance between two ions = 72 + 140 pm = 212 pm
Force = 8.99 x 10^9 X 2 X 1.9 x 10^-19 C X 2 X 1.9 x 10^-19 C / (212 X 10^-12 )^2
Force = 0.002889 X 10^-5 = 2.889 X 10^-8 N
