Which one of the following does not readily give oxygen upon heating?

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

In the given reaction,$A$ is:
$A$ $\xrightarrow{\text{Reduction}} B$ $\xrightarrow{HNO_2} C_2H_5OH$

In which of the following reactions does the hybridisation of the central atom change from $sp^2$ to $sp^3$?

The vapour pressure in $mm$ of $Hg$,of an aqueous solution obtained by adding $18 \ g$ of glucose $(C_6H_{12}O_6)$ to $180 \ g$ of water at $100^{\circ} C$ is

Indicate the number of unpaired electrons in:
$(a)$ $P$ $(b)$ $Si$ $(c)$ $Cr$ $(d)$ $Fe$ and $(e)$ $Kr$