What is the surface charge density on this face of the penny?

The equation for surface charge density is η = Q/A. Since the electric field is just above the face of the penny, the penny can be modeled as an infinite plane of charge Eplane = η/(2ε0). Combining these equations will result in Eplane = Q/(A⋅2⋅ε0). Rearranging this equation to find the surface charge density will be (Q/A) = (Eplane⋅2⋅ε0). However, this will be the surface charge density for both sides of the penny. In order to find the surface charge density of only one side of the penny, divide Eplane⋅2⋅ε0 by 2.

Source https://www.physicsforums.com/threads/what-is-the-surface-charge-density-on-the-face-of-the-penny.904118/

Answertechnician (a) is correct;