What is the correct order of stability for the superoxides?

White metal is an alloy of

The correct statements are:
$I$. The low solubility of $LiF$ is due to its high lattice enthalpy.
$II$. $LiBr$ is soluble in acetone.
$III$. $LiCl$ is soluble in pyridine.
$IV$. The order of melting points of alkali metal halides is $MF > MCl > MBr > MI$.

If $Na$ is heated in the presence of air,it forms:

Which of the following elements does not exhibit variable valency?

Alkali metals possess metallic lustre when freshly cut because