Heating $(NH_4)_2Cr_2O_7$ liberates a gas. The same gas is obtained by:

Which of the following nitrogen trihalides is the weakest base?

$Cu +$ conc. $HNO_3$ (hot) $\rightarrow Cu(NO_3)_2 + X$ (oxide of nitrogen);
then $X$ is

$PbO_2$ is

In group $-15$,as we move from $N$ to $Bi$,the $M_2O_3$ type oxides become ...... .

Phosphorus has three allotropic forms:
$(i)$ white phosphorus
$(ii)$ red phosphorus and
$(iii)$ black phosphorus.
Write the difference between white and red phosphorus on the basis of their structure and reactivity.