There are three optical media 1, 2 and 3 with their refractive indices ${\mu }_1>{\mu }_2>{\mu }_3\cdot (\mathrm{TIR}\to$ total interned reflection).

when a ray of light travels from 3 to 1 no TIR will take place

critical angle between 1 and 2 is less than the critical angle between l and 3

critical angle between 1 and 2 is more than the critical angle between 1 and 3

chances of TIR are more when ray of light travels from 1 to 3 as compare to the case when it travel from 1 to 2