The correct option is D 1.28×105 N/C
For any spherical conductor, if it has any charge, the charge will reside on the surface of the conductor.
Given, radius of conductor is 10 cm and we have to find electric field at distance of 15 cm.
So, we can assume the sphere as point charge to calculate the electric field at distance of 15 cm.
r=15 cm=0.15 m