Which element from the following combines with hydrogen to form a compound with the lowest thermal stability?

The thermally most stable compound is:

Who established the elemental nature of chlorine?

Aqua regia is a mixture of

Which of the following reactions proves the chlorinating property of phosphorus pentachloride?

Which of the following reactions are correct with respect to the formation of products?
$I$. $2 NaOH + SO_2 \longrightarrow Na_2SO_3 + H_2O$
$II$. $XeF_4 + O_2F_2 \stackrel{143 K}{\longrightarrow} XeF_6 + O_2$
$III$. $PCl_5 + 4 H_2O \longrightarrow H_3PO_4 + 5 HCl$
$IV$. $2 NaNO_2 + 2 HCl \longrightarrow 2 NaCl + NO + NO_2 + H_2O$