The ray diagram for two lenses kept at some distance is given in the figure. Which of the following options is correct? ($f_1, f_2 =$ focal lengths,$d =$ distance between lenses)

What is the power of the combination of a convex lens and a concave lens of equal focal length $25 \text{ cm}$?

An optician makes spectacles having a combination of a convex lens of focal length $40 \ cm$ in contact with a concave lens of focal length $25 \ cm$. The power of this combination of lenses in dioptre is:

Assertion: Two convex lenses joined together cannot produce an achromatic combination.
Reason: The condition for achromatism is $\frac{\omega_1}{f_1} + \frac{\omega_2}{f_2} = 0$,where symbols have their usual meaning.

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

The plane faces of two identical plano-convex lenses,each having a focal length of $40 \ cm$,are pressed against each other to form a biconvex lens. The distance from this lens at which an object must be placed to obtain a real,inverted image with a magnification of $1$ is ....... $cm$.