The temperature required for electrolysis is maximum for which of the following hydrides?

Cyclic polymetaphosphates have the general formula of $[P_nO_{3n}]^{n-}$. Cyclic trimeric polymetaphosphate $(P_3O_9)^{3-}$ has commercial importance. Which of the following is not true regarding $P_3O_9^{3-}$?

In case of nitrogen,$NCl_3$ is possible but not $NCl_5$,while in case of phosphorus,$PCl_3$ as well as $PCl_5$ are possible. This is due to:

$A$ obtained by Ostwald's method involving air oxidation of $NH_3$,upon further air oxidation produces $B$. $B$ on hydration forms an oxoacid of Nitrogen along with evolution of $A$. The oxoacid also produces $A$ and gives positive brown ring test.

Metaphosphoric acid has the formula

Which of the following statements is $NOT$ true for both white and red phosphorus?