When a ray of light is incident on a plane mirror, it follows the law of reflection, which states that the angle of incidence is equal to the angle of reflection. In this case, the ray of light is incident on the mirror at an angle of 30° with the normal (a line perpendicular to the mirror surface) at the point of incidence.

Since the angle of incidence and the angle of reflection are equal, the ray of light will be deviated from its incidence direction by an angle of 30°. However, this deviation is on the same side as the incident ray, so the actual angle of deviation will be the sum of the angle of incidence and the angle of reflection, which is 30° + 30° = 60°.

Therefore, option 2, 60°, is the correct answer. Option 1, 30°, is incorrect because it only represents the angle of incidence, not the deviation. Option 3, 120°, is incorrect because it implies a complete reversal in the direction of the reflected ray, which is not the case for a plane mirror. Option 4, None of these, is also incorrect because option 2, 60°, is the correct answer.