By the action of hot conc. $H_2SO_4,$ phosphorus changes to

Under which conditions can active nitrogen be obtained from $N_2$ gas using an electric spark?

Nitrogen forms how many oxides?

When orthophosphoric acid is heated to $600\,^{\circ}C,$ the product formed is

Based on the compounds of group $15$ elements,the correct statement$(s)$ is (are):
$(A)$ $Bi_2O_5$ is more basic than $N_2O_5$
$(B)$ $NF_3$ is more covalent than $BiF_3$
$(C)$ $PH_3$ boils at a lower temperature than $NH_3$
$(D)$ The $N-N$ single bond is stronger than the $P-P$ single bond

Which of the following combines with $Fe(II)$ ions to form a brown complex?