The correct option is D 10 N/C
Given:
Thickness of sheet, d=4 cm
Distance of point P from mid-line of sheet, x=1 cm=0.01 m
Charge density, ρ=9 nC/m3
Here, x<d2
We know that the electric field inside the non-conducting thick sheet, at a distance x from the central plane, is given by,
E=ρxϵ0
⇒E=9×10−9×0.019×10−12=10 N/C
So, option (d) is correct.