The refractive indices of glass and water with respect to air are $3/2$ and $4/3$ respectively. The refractive index of glass with respect to water is:

$A$ ray of light passes through four transparent media with refractive indices $\mu_1, \mu_2, \mu_3$ and $\mu_4$ as shown in the figure. The surfaces of all media are parallel. If the emergent ray $CD$ is parallel to the incident ray $AB$,we must have

The distance travelled by light in glass (refractive index $= 1.5$) in a nanosecond will be.......$cm$.

$A$ ray of monochromatic light is incident on the plane surface of separation between two media $X$ and $Y$ with angle of incidence $i$ in medium $X$ and angle of refraction $r$ in medium $Y$. The given graph shows the relation between $\sin i$ and $\sin r$. If $V_X$ and $V_Y$ are the velocities of the ray in media $X$ and $Y$ respectively, then which of the following is true?

The wavelength of sodium light in air is $5890 \ \mathring{A}$. The velocity of light in air is $3 \times 10^8 \ m/s$. The wavelength of light in a glass of refractive index $1.6$ would be close to......$\mathring{A}$

Give one example of a substance whose mass density is low but optical density is high.