What type of image cannot be formed by a convex lens?

The laws of reflection hold good for

The absolute refractive indices of glass and water are $4/3$ and $3/2$ respectively. If the speed of light in glass is $2 \times 10^{8} \ m \ s^{-1}$,calculate the speed of light in $(i)$ vacuum,$(ii)$ water.

Which of the following has the minimum refractive index?

How can you identify the three types of mirrors without touching them?

An object is placed at the following distances from a concave mirror of focal length $15 \, cm$.
$(a)$ $10 \, cm$ $(b)$ $20 \, cm$ $(c)$ $30 \, cm$ $(d)$ $40 \, cm$
Which position of the object will produce:
$(1)$ Virtual image
$(2)$ $A$ diminished real image
$(3)$ An enlarged real image
$(4)$ An image of same size