Which of the following fluorides does not exist?

How many types of sporophylls are found in Pteridophytes?

Two wires of the same material have lengths in the ratio $1:2$ and their radii are in the ratio $1:\sqrt{2}$. If they are stretched by applying equal forces,the increase in their lengths will be in the ratio:

In Kranz anatomy,the bundle sheath cells have

Find the $g.c.d.$ and $l.c.m.$ using the fundamental theorem of arithmetic for the numbers: $24$,$36$,and $60$.

$A$ thin spherical conducting shell of radius $R$ has a charge $q$. Another charge $Q$ is placed at the centre of the shell. The electrostatic potential at a point $P$ at a distance $R/2$ from the centre of the shell is