There is a critical angle i _{�c �}. If the angle of incidence is greater than the critical angle, there is no refraction but only internal reflection. If the observer is placed such that the refracted rays (that are coming from the incident rays with angle of incidence greater than the critical angle) can’t reach their/his/her eyes, then the pin will not be observed. Otherwise, we can see from the ray diagram that the image of the pin is closer to A. Hence, (b) is correct. If the incident ray hits at an angle greater than the critical angle, there will be no refraction. Thus, light will not reach the observer. Thus, (d) is also correct. The image isn’t closer to D; hence, (b) is incorrect. Also, image in not formed at the centre of AD; hence, (c) is also incorrect.