How many $P-O-P$ linkages are there in $P_4O_{10}$?

The decreasing order of the number of ionisable hydrogen atoms in the following molecules is:
$I$. $H_3PO_4$
$II$. $H_3PO_3$
$III$. $H_3PO_2$
$IV$. $H_4P_2O_6$

Assertion $(A)$: In group $15$ elements,nitrogen does not form pentahalides.
Reason $(R)$: Nitrogen can exhibit $+5$ oxidation state.
The correct option among the following is:

The correct code for stability of oxidation states for given cations is:
$(i)$ $Pb^{2+} > Pb^{4+}, Tl^{+} < Tl^{3+}$
$(ii)$ $Bi^{3+} < Sb^{3+}, Sn^{2+} < Sn^{4+}$
$(iii)$ $Pb^{2+} > Pb^{4+}, Bi^{3+} > Bi^{5+}$
$(iv)$ $Tl^{3+} < In^{3+}, Sn^{2+} > Sn^{4+}$
$(v)$ $Sn^{2+} < Pb^{2+}, Sn^{4+} > Pb^{4+}$
$(vi)$ $Sn^{2+} < Pb^{2+}, Sn^{4+} < Pb^{4+}$

Which of the following mixtures of two gases in equimolar amounts will produce a blue liquid at $-30\,^oC$?

Which form of phosphorus is thermodynamically most stable?