What is thick lens? How it is different from the thin lens?

In the given figure, what is the angle of prism?

A thin prism of angle $6°$ made up of glass of refractive index $1.5$ is combined with another prism made up of glass of refractive index $1.75$ to produce dispersion without deviation. Then find the angle of the second prism.

Two thin lenses are in contact with each other. One of these is a concave lens of focal length $20 \mathrm{cm}$ and the other is a convex lens of the same focal length. Determine the focal length of the combination and state how it behaves.

The word $"\mathrm{KVPY}"$is written on board and viewed through different lenses such that board is at a distance beyond the focal length of the lens.

Ignoring magnification effects, consider the following statements.
$\left(\mathrm{I}\right)$ Image $\left(\mathrm{i}\right)$ has been viewed from the planar side of a plano-convex lens and image
$\left(\mathrm{ii}\right)$ from the convex side of a plano-convex lens.
$\left(\mathrm{II}\right)$ Image $\left(\mathrm{i}\right)$ has been viewed from the concave side of a plano-concave lens and image $\left(\mathrm{ii}\right)$ from the convex side of a plano-convex lens.
$\left(\mathrm{III}\right)$ Image $\left(\mathrm{i}\right)$ has been viewed from the concave side of a plano-concave lens and image $\left(\mathrm{ii}\right)$ from the planar side of a plano-convex lens. $\left(\mathrm{IV}\right)$ Image$\left(\mathrm{i}\right)$ has been viewed from the planar side of a plano-concave lens and image $\left(\mathrm{ii}\right)$ from the convex side of a plano-convex lens.
Which of the above statements are correct?