Mercury is a liquid at $0 \, ^\circ C$ because of

Select the correct option.

Which of the following orders is correct for the property given?

Match the following properties with the corresponding metals:

Property	Metal
$a$. Element with highest second ionization enthalpy $(\Delta_{i} H_2)$	$i$. $Co$
$b$. Element with highest third ionization enthalpy $(\Delta_{i} H_3)$	$ii$. $Cr$
$c$. $M$ in $[M(CO)_6]$	$iii$. $Cu$
$d$. Element with highest heat of atomization $(\Delta_{a} H)$	$iv$. $Zn$
	$v$. $Ni$

Which of the comparison regarding $Zn, Cd, Hg$ is/are incorrect?
$(I)$ $ZnCl_2$ is ionic whereas $CdCl_2$ and $HgCl_2$ are covalent
$(II)$ $Zn$ and $Cd$ dissolve in dilute acid $(HCl)$ liberating $H_2$ but $Hg$ cannot
$(III)$ $Zn$ and $Cd$ form white ppt. of $Zn(OH)_2$ and $Cd(OH)_2$ but $Hg$ forms coloured ppt. of $HgO$ or $Hg(OH)_2$
$(IV)$ All form $M_2^{2+}$ type ion

Identify the $incorrect$ order of the given parameter.