When can it be assumed that light moves in a straight line?

$A$ 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 bottom of a container filled with liquid appears slightly raised because of

In the figure shown,$\frac{\sin i}{\sin r}$ is equal to:

The refractive index of glass is $1.5$ and that of water is $1.3$. If the speed of light in water is $2.25 \times 10^8 \, m/s$,what is the speed of light in glass?

$A$ tank is filled with water to a height of $12.5 \;cm$. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be $9.4 \;cm$. What is the refractive index of water?
If water is replaced by a liquid of refractive index $1.63$ up to the same height,by what distance would the microscope have to be moved to focus on the needle again?