The following figure represents two biconvex lenses $$L_1$$ and $$L_2$$ having focal length $$10 \mathrm{~cm}$$ and $$15 \mathrm{~cm}$$ respectively. The distance between $$L_1$$ & $$L_2$$ is :

Given below are two statements :

Statement (I) : When an object is placed at the centre of curvature of a concave lens, image is formed at the centre of curvature of the lens on the other side.

Statement (II) : Concave lens always forms a virtual and erect image.

In the light of the above statements, choose the correct answer from the options given below :

The position of the image formed by the combination of lenses is :

Critical angle of incidence for a pair of optical media is $$45^{\circ}$$. The refractive indices of first and second media are in the ratio: