Statement I: A plane wave passing through a prism remains a plane wave due to refraction at parallel surfaces. However, when passing through a small pin hole comparable to the wavelength, Huygens' principle applies where each point on the wavefront acts as a source of secondary wavelets, creating a spherical wavefront. Statement I is TRUE.
Statement II: When a spherical wave emerges from a slit, the diffraction effect depends on slit width. A narrower slit causes stronger diffraction and greater curvature of the emerging wavefront. As slit width increases, diffraction effects decrease and the wavefront becomes flatter with reduced curvature. Therefore, the curvature decreases with increasing slit width. Statement II is FALSE.
The correct answer identifies that Statement I is true but Statement II is false.