The image shows the path of light as it travels from one medium to another.
$(9)$ What are medium $1$ and medium $2$?

	Medium $1$	Medium $2$
$A$.	Water	Kerosene
$B$.	Kerosene	Diamond
$C$.	Flint glass	Water
$D$.	Kerosene	Flint glass

$(10)$ The power of a lens $(P)$ is calculated by the formula, $P = \frac{1}{f}$, where $f$ is the focal length of the lens in meters. A lens has a focal length of $-0.25 \ m$. Is it a convex lens or a concave lens? Explain your answer.

(N/A) $(9)$ $C$. Flint glass/Water. In the image, the refracted ray bends away from the normal, which indicates that light is traveling from a denser medium to a rarer medium. Among the options, flint glass (refractive index $\approx 1.65$) is denser than water (refractive index $\approx 1.33$).
$(10)$ The lens is a concave lens.
Step $1$: The formula for power is $P = \frac{1}{f}$.
Step $2$: Given $f = -0.25 \ m$.
Step $3$: Since the focal length is negative, the power $P = \frac{1}{-0.25} = -4 \ D$ is also negative.
Step $4$: By sign convention, concave lenses have a negative focal length and negative power, while convex lenses have a positive focal length and positive power.