Final answer:
The normal force, represented as 0N, is equal to the weight (mass x acceleration due to gravity) when the surface is horizontal with an angle of 0 degrees.
Step-by-step explanation:
To understand why 0N is the correct answer, we need to look at the formula and the given information. In the given equation, N cos 0 = mg, we can see that N is the normal force, 0 is the angle between the surface and the horizontal, m is the mass, and g is the acceleration due to gravity. The cosine of 0 is 1 when 0 is 0 degrees, which means that N cos 0 becomes N. Therefore, when the surface is horizontal (0 = 0 degrees), the normal force N is equal to mg, which is why 0N is the correct answer.