How many types of sporophylls are found in Pteridophytes?

Which one of the following has maximum genetic diversity in India?

If $\frac{3x}{(x-a)(x-b)} = \frac{2}{x-a} + \frac{1}{x-b}$,then $a:b$ is equal to

An electric dipole is placed along the $x$-axis at the origin $O$. $A$ point $P$ is at a distance of $20 \ cm$ from this origin such that $OP$ makes an angle $\frac{\pi}{3}$ with the $x$-axis. If the electric field at $P$ makes an angle $\theta$ with the $x$-axis,the value of $\theta$ would be

Which one of the following is correct about the stability of the given ions?

How many bridging oxygen atoms are present in $P_4O_{10}$?