For a ray of light, the critical angle is minimum, when it travels from

Step-by-step solution

The critical angle (c ) for total internal reflection (TIR) when light travels from a medium of refractive index (n₁ ) to a medium of lower refractive index (n₂ ) is given by ( c= n₂ n₁ ) where (n₁>n₂ ). The smaller the ratio ( n₂ n₁ ), the smaller ( c ), and hence the smaller the critical angle (c ). From the options, the valid scenarios for TIR are only those in which the first medium has a higher index than the second. That is: ( aligned & Glass to air (n_ glass 1.5, n_ air 1.0 ) & c= 1.0 1.5 = 2 3 c 42^ aligned