In the Ostwald's process for the manufacture of $HNO_3$,the catalyst used is

With reference to protonic acids,which of the following statements is correct?

The products formed by complete hydrolysis of $PCl_3$ are

An orange solid $(X)$ on heating,gives a colourless gas $(Y)$ and a green residue $(Z).$ Gas $(Y)$ on treatment with $Mg,$ produces a white solid substance. Identify the white solid substance.

The molecular formula of metaphosphoric acid is

The total number of $\sigma$ and $\pi$-bonds in pyrophosphoric acid are respectively