A convex lens of power $P$ is immersed in water. How will its power change?

A convex lens is made up of three different materials as shown in the figure. For a point object placed on its axis, the number of images formed is

A biconvex lens is cut into two halves along $\left(\mathrm{i}\right) XOX\text{'}$ and $\left(\mathrm{ii}\right) YOY\text{'}$ as shown in the figure. Let $f$, $f\text{'}$, $f\text{'}\text{'}$ be the focal lengths of the complete lens, of each half in case $\left(\mathrm{i}\right)$, and of each half in case $\left(\mathrm{ii}\right)$, respectively. Choose the correct statement from the following:-