What is the power of a plane glass sheet?

Where should an object be placed in front of a convex lens to get a real image of the size of the object?

What is the power of a convex lens with a focal length of $20 \text{ cm}$?

What is the power of a concave lens of focal length $25\, cm$?

With the help of a ray diagram,show the formation of an image by a convex lens when the object is placed between $F$ and $2F$. Write two characteristics of the image so formed.

Name the type of lens that can be used to obtain:
$(i)$ $A$ magnified and virtual image.
$(ii)$ $A$ diminished and virtual image of the object.