Critical angle of incidence for a pair of optical media is $45^{\circ}$. The refractive indices of the first and second media are in the ratio:

$A$ wide slab consisting of two media of refractive indices $n_1$ and $n_2$ is placed in air as shown in the figure. $A$ ray of light is incident from medium $n_1$ to $n_2$ at an angle $\theta$,where $\sin \theta$ is slightly larger than $1/n_1$. Take the refractive index of air as $1$. Which of the following statement$(s)$ is(are) correct?
$(A)$ The light ray enters air if $n_2 = n_1$
$(B)$ The light ray is finally reflected back into the medium of refractive index $n_1$ if $n_2 < n_1$
$(C)$ The light ray is finally reflected back into the medium of refractive index $n_1$ if $n_2 > n_1$
$(D)$ The light ray is reflected back into the medium of refractive index $n_1$ if $n_2 = 1$

$A$ ray of light travels from a denser medium to a rarer medium. The reflected and the refracted rays are perpendicular to each other. If '$i$' and '$r_1$' are the angle of incidence and angle of refraction respectively and '$C$' is the critical angle,then the angle of incidence is

$A$ material is embedded between two glass plates. The refractive index $n$ of the material varies with thickness as shown in the figure. The maximum incident angle (in degrees) on the material for which the beam will pass through the material is

$A$ ray of light propagates from glass (refractive index $= 3/2$) to water (refractive index $= 4/3$). The value of the critical angle is:

Assertion: The maximum refractive index of the liquid for total internal reflection of the ray passing through the prism as shown in the figure must be $\sqrt 2$.
Reason: Here,the critical angle is $45^o$.