The point where the alignment changes from a straight line or tangent to a circular curve is called as-

Correct option is B

The Point of Curvature (PC) is the point where the alignment changes from a straight line (or tangent) to a circular curve. This is a critical point in road and railway design where the straight alignment transitions into the curved path.
 Point of commencement: Incorrect, this term generally refers to the start of a project or construction work.
 Point of curvature: Correct, as this is where the alignment changes from a tangent to a curve.
 Point of tangency: This is the point where the curve ends and the alignment returns to a straight tangent.
 Finishing mark: Not a standard term used in this context.
Therefore, the correct answer is (b) Point of curvature.