Consider the Earth to Have a Uniformly Charged Surface with Density

Multiple Choice

Consider the Earth to have a uniformly charged surface with density $\sigma$ per unit area.What is the value of $\sigma$ if objects near the surface,carrying charge Q and having mass m,experience no net force?

A) + $\varepsilon$ ₀._omg/Q
B) - $\varepsilon$ ₀._omg/Q
C) + 2 $\varepsilon$ ₀._omg/Q
D) -2 $\varepsilon$ ₀._omg/Q
E) Either A or B is correct,depending on the sign of Q.