The oxide which forms a dimer is

The reaction of $NO$ with $N_2O_4$ at $250 \ K$ gives :

White phosphorus,when heated with conc. $NaOH$ solution in an inert atmosphere of $CO_2$,forms phosphine and a sodium salt of oxoacid of phosphorus,$'X'$. The oxidation state of phosphorus in $'X'$ is

The following statements concern elements in the periodic table. Which of the following is true?

In the following reaction,assign the correct option for the underlined atom in the product of complete hydrolysis at $R.T.$:
$\underline{N}_2O_3 + H_2O \longrightarrow 2HNO_2$

The most stable hydride is