At what angle should an unpolarised beam be incident on a crystal of refractive index $\mu = \sqrt{3}$,so that the reflected beam is completely polarised (in $^o$)?

Which one of the following types of organisms occupy more than one trophic level in a pond ecosystem?

$A$ point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at distances of $2 \ m$ and $3 \ m$ respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is

If the difference between the roots of $x^2+ax+b=0$ and $x^2+bx+a=0$ is the same,and $a \neq b$,then:

Which one of the following orders presents the correct sequence of the increasing basic nature of the given oxides?

Which alga exhibits a haplo-diplontic life cycle?