Which of the following is metaphosphoric acid?

Which of the following is used in the industrial production of nitric acid by the Ostwald process?

The following are some statements related to $VA$ group hydrides:
$I$. Reducing property increases from $NH_3$ to $BiH_3$.
$II$. Tendency to donate lone pair decreases from $NH_3$ to $BiH_3$.
$III$. Thermal stability of hydrides decreases from $NH_3$ to $BiH_3$.
$IV$. Bond angle of hydrides decreases from $NH_3$ to $BiH_3$.
The correct statements are:

Ionic radius (in $\mathring{A}$) of $As^{3+}$,$Sb^{3+}$ and $Bi^{3+}$ follow the order:

Which of the following substances is not an isomorphous true alum and is known as a pseudo alum?

When orthophosphoric acid is heated to $600\,^oC$,it forms .................. .