Which of the following statements are correct about $Zn,\,Cd$ and $Hg$ ?

$(I)$ they exhibit high enthalpies of atomisation as the $d-$ subshell is full

$(II)$ $zn$ and $Cd$ do not show variable oxidation states while $Hg$ shows $+ I$ and $+ II$

$(III)$ Compound of $Zn,\,Cd$ and $Hg$, are paramagnetic in nature

$(IV)$ $Zn,\,Cd$ and $Hg$ are called soft metals

• A

  $I,\,II,\,III$

• B

  $I,\,III$

• C

  $II,\,IV$

• D

  $IV$ only