What type of lens behaviour will an air bubble inside water show?

What can be said about the magnification of an image formed by a convex mirror?

$A$ point object is placed at a distance of $12 \, cm$ from a convex lens on its principal axis. Its image is formed on the other side of the lens at a distance of $18 \, cm$ from the lens. Find the focal length of the lens. Is the image magnified? Justify your answer.

$A$ ray of light is incident on a plane mirror normally. What are the angle of incidence and the angle of reflection?

$(a)$ Write one use of a concave mirror as well as a convex mirror.
$(b)$ Draw ray diagrams for the following cases when a ray of light:
$(i)$ passing through the centre of curvature of a concave mirror is incident on it.
$(ii)$ parallel to the principal axis is incident on a convex mirror.
$(iii)$ is incident at the pole of a convex mirror.
$(iv)$ passing through the focus of a concave mirror is incident on it.

$A$ concave mirror and a convex lens are held in water. What changes, if any, do you expect in their focal length?