Which of the following elements is the most metallic?

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.

What is the number of oxygen atoms attached to each phosphorus atom in $P_4O_{10}$?

Which one of the following is used to remove moisture from ammonia gas?

Identify the reaction which does not liberate $N_2$.

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