Which of the following conditions are necessary and sufficient for total internal reflection to take place at the boundary between two optical media? i. lig...

Which of the following conditions are necessary and sufficient for total internal reflection to take place at the boundary between two optical media? i. light is passing from optically denser medium to optically less dense medium. ii. light is passing from optically less dense medium to optically denser medium. iii. angle of incidence is greater. iv. angle of incidence is lesser