1) convex mirror diverges and reflects the rays falling on it, and hence it always gives a virtual image.
Concave lens transmits the light rays to the other side and diverges them. So only a virtual image is formed.
Speed of light in a medium = speed of light in vacuum / refractive index
Since refractive index is less in Kerosene, the speed of light is more in kerosene.
The boiling point decreases at higher altitudes, as the atmospheric pressure of air is less.