What is the speed of light waves in a vacuum in units of $km/s$?

$A$ candle is placed at a distance of $10 \ cm$ from a plane mirror. At what distance from the mirror will the image of this candle be formed (in $cm$)?

The image of an object formed by a plane mirror is due to which optical phenomenon?

$(a)$ $A$ ray of light falls normally on a face of a glass slab. What are the values of angle of incidence and angle of refraction of this ray?
$(b)$ Light enters from air to a medium $X$. Its speed in medium $X$ becomes $1.5 \times 10^{8} \ m \ s^{-1}$. Speed of light in air is $3 \times 10^{8} \ m \ s^{-1}$. Find the refractive index of medium $X$.

Which of the following has the minimum refractive index?

Where is the image formed when an object is placed between the principal focus $(F)$ and the center of curvature $(C)$ of a concave mirror?