Which of the following oxides of nitrogen is a blue solid?

The stable bivalency of $Pb$ and trivalency of $Bi$ is

In the nitrogen family,the $H-M-H$ bond angle in the hydrides $MH_3$ gradually becomes closer to $90^o$ on going from $N$ to $Sb$. This shows that gradually

Which of the following phosphorus oxyacids can act as a reducing agent?

Which among the following oxoacids of phosphorus will have $P-O-P$ bonds?
$I$. $H_4P_2O_5$
$II$. $H_4P_2O_6$
$III$. $H_4P_2O_7$
$IV$. $(HPO_3)_3$

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