Which of the following oxides is most acidic?

The number of bridged oxygen atoms present in compound $B$ formed from the following reactions is
$Pb(NO_3)_2 \xrightarrow{673 \ K} A + PbO + O_2$
$A \xrightarrow{\text{Dimerise}} B$

Among the hydrides $NH_3, PH_3,$ and $BiH_3$,the hydride with the highest boiling point is $X$ and the hydride with the lowest boiling point is $Y$. What are $X$ and $Y$ respectively?

In the Ostwald process for the manufacture of $HNO_3$,which of the following is used as a catalyst?

Given below are two statements:
Statement $I$: The $N-N$ single bond is weaker and longer than the $P-P$ single bond.
Statement $II$: Compounds of group $15$ elements in $+3$ oxidation state readily undergo disproportionation reactions.
In the light of the above statements,choose the correct answer from the options given below:

Nitric oxide $(NO)$ is prepared by the action of dilute $HNO_3$ on which of the following metals?