Which of the following substances gives oxygen upon moderate heating?

The correct order of $K_a$ in aqueous solution at $298 \ K$.

Although fluorine is more electronegative than oxygen,the ability of oxygen to stabilize higher oxidation states exceeds that of fluorine. Why?

The oxoacid of sulphur that does not contain a bond between sulphur atoms is

White phosphorus reacts with sulphuryl chloride to form $PCl_5$ and $X$. Chlorine reacts with $X$ in the presence of wood charcoal to form $Y$. $X$ and $Y$ are respectively

$H_2S$ is less acidic than $H_2Te$. Why?