The number of hydroxyl groups in pyrophosphoric acid is ......... .

Sodium nitrite is reacted with $H_2SO_4$ to form $NaHSO_4$,$HNO_3$,water and $X$. Gold is dissolved in aqua regia to form water,$AuCl_4^{-}$ and $Y$. $X$ and $Y$ are respectively

Which of the following statements is correct for $PH_3$?

Which of the following does not produce $N_2$ gas on heating?

The molecular formula of an acid of phosphorus is $H_3PO_2$. What are its name and basicity,respectively?

The structural formula of hypophosphorus acid is