$A$ convex lens and a concave lens,each having the same focal length of $25\, cm$,are put in contact to form a combination of lenses. The power in diopters of the combination is:

$A$ convex lens $A$ of focal length $20 \, cm$ and a concave lens $B$ of focal length $5 \, cm$ are kept along the same axis with a distance $d$ between them. If a parallel beam of light falling on $A$ leaves $B$ as a parallel beam,then the distance $d$ in $cm$ will be:

Two thin plano-convex lenses each of focal length $f$ are placed as shown in the figure. The ratio of their effective focal lengths in the three cases is

$A$ concave and a convex lens have the same focal length of $20 \ cm$ and are put into contact to form a lens combination. The combination is used to view an object of $5 \ cm$ length kept at $20 \ cm$ from the lens combination. As compared to the object,the image will be

$A$ lens of power $+2$ diopters is placed in contact with a lens of power $-1$ diopter. The combination will behave like

Four combinations of two thin lenses are given in List-$I$. The radius of curvature of all curved surfaces is $r$ and the refractive index of all lenses is $1.5$. Match lens combinations in List-$I$ with their focal length in List-$II$ and select the correct answer using the code given below the lists.