If $x > 0, y > 0, z > 0, xy + yz + zx < 1$ and if $\tan^{-1} x + \tan^{-1} y + \tan^{-1} z = \pi$,then $x + y + z$ equals to

Which of the following is an incorrect pair regarding lichens?

Which of the following liquid mixtures shows a positive deviation from Raoult's law?

The major product of the following reaction is

$A$ compound of mercury used in cosmetics,in Ayurvedic and Yunani medicines and known as Vermilion is

The volume of an air bubble becomes three times as it rises from the bottom of a lake to its surface. Assuming atmospheric pressure to be $75\, cm$ of $Hg$ and the density of water to be $1/10$ of the density of mercury,the depth of the lake is ....... $m$.