Which of the following, on simply heating in air, gives the metal directly through auto-reduction?

Answer: B

Mercury(II) oxide is unstable on heating, so

HgS + O X_{2} Hg + SO X_{2}

gives the metal directly.

ZnS

and

FeS X_{2}

give stable oxides,

ZnO

and

Fe X_{2} O X_{3}

, that need a reducing agent, and

CuFeS X_{2}

on roasting gives

Cu X_{2} S

FeS

and

SO X_{2}

, not the metal.