$\textit{a.}$, Principal focus is placed on the both sides of the converging lens.

Their distance from the centre is equal on the both sides.

Parallel incident ray of light on the left side will converge into the focus on the right side and vice versa.

$\textit{b.}$, Principal focus of a diverging lens is located on the both sides of the converging lens.

Distance from the centre is equal on the both sides.

Parallel incident ray of light on the left side will diverge into the focus on the left side and vice versa.

$\textit{c.}$, Diverging lens differ from converging lens because of the image which is formed and because diverging lens spreads a beam of light and converging one focuses them.

a. The principal foci are present on both sides of the converging lens. They are equidistant from the center of the lens on its either sides. A parallel beam of light entering the lens from its left side converges to the focus on its right side while a parallel beam of light entering the lens from its right side converges to the focus on its left side.