If the angle between the straight line joining foci and the ends of the minor axis of the ellipse $\large\frac{x^2}{a^2}+\frac{y^2}{b^2}$$=1$ is $90^{\large\circ}$ .Find its eccentricity?

Question

$\begin{array}{1 1}(a)\;\large\frac{1}{\sqrt 2}\\(b)\;\large\frac{1}{\sqrt 5}\\(c)\;\large\frac{3}{\sqrt 2}\\(d)\;\large\frac{5}{\sqrt 2}\end{array}$