For what position of the object does a concave mirror form a real and diminished image?

$(a)$ Explain the following terms related to spherical lenses:
$(i)$ Optical centre
$(ii)$ Centres of curvature
$(iii)$ Principal axis
$(iv)$ Aperture
$(v)$ Principal focus
$(vi)$ Focal length
$(b)$ $A$ converging lens has a focal length of $12 \, cm$. Calculate at what distance should the object be placed from the lens so that it forms an image at $48 \, cm$ on the other side of the lens.

The image formed by a convex spherical mirror is always:

If an object is placed symmetrically between two plane mirrors, inclined at an angle of $72^{\circ},$ then the total number of images formed is

$A$ plane mirror is placed vertically facing due north. An arrow pointing north-east is kept in front of the mirror. In which direction will the arrow point in this image?

Where does an object and its image coincide in a concave mirror?