CONCEPT: Total Internal Reflection (TIR): [ alt="F1 P.Y Madhu 12.05.20 D1" src="//storage.googleapis.com/tb-img/production/20/05/F1_P.Y_Madhu_12.05.20_D1.png" style="width: 412px; height: 257px;"> When a ray of light goes from denser to the rarer medium it bends away from the normal and as the angle of incidence in denser medium increases, the angle of refraction in the rarer medium also increases and at a certain angle, angle of refraction becomes 90°, this angle of incidence is called critical angle (C). When Angle of incidence exceeds the critical angle than light ray comes back into the same medium after reflection from the interface. This phenomenon is called Total internal reflection (TIR). Conditions for TIR: The ray must travel from denser medium to rarer medium. The angle of incidence i must be greater than the critical angle C. EXPLANATION: The formation of mirage in the desert is formed because of Total Internal Reflection. Therefore statement 1 is correct.\ The formation of the image in the microscope is due to the refraction of light. Therefore statement 2 is incorrect. The color of the evening sky is due to atmospheric reaction. Therefore statement 3 is incorrect. Optical fiber works on the principle of total internal reflection. Therefore statement 4 is correct.