The student R has performed the experiment methodically. The reason can be explained using Snell's law. According to Snell's law, sini*sinr=μg Here, i = Angle of incidence r = Angle of refraction μg = Refractive index for glass The angle of refraction measured by student R is most appropriate as it verifies the Snell's law. Given: i = 40o The angle of refraction measured by student R, r = 25o. Also, sin40o = 0.642 sin25o = 0.422 Now, sin40osin25o=0.6420.422=1.52 The refractive index for glass is 1.5; it verifies the result derived above. Hence, the correct option is C. Disclaimer: The values of sin40o and sin25o can be obtained using trigonometric tables.