$A$ horizontal tube of non-uniform cross-section has radii of $0.2\,m$ and $0.1\,m$ at points $P$ and $Q$ respectively. For streamline flow of an incompressible liquid, the rate of liquid flow is:

The oxidation state and covalency of $Al$ in $[AlCl(H_2O)_5]^{2+}$ are respectively

Which of the following statements is true?

Two polaroids are placed in the path of an unpolarized beam of intensity $I_0$ such that no light is emitted from the second polaroid. If a third polaroid,whose polarization axis makes an angle $\theta$ with the polarization axis of the first polaroid,is placed between these polaroids,then the intensity of light emerging from the last polaroid will be:

In a $\triangle ABC$,if $\frac{a}{b^2-c^2} + \frac{c}{b^2-a^2} = 0$,then $B$ is equal to

If the direction cosines of two lines are given by $l+m+n=0$ and $l^2-5m^2+n^2=0$,then the angle between them is