Question
Among the following configurations, the element which has the highest electron affinity is
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$W + {O_2}\, \rightleftharpoons X$
$X + {H_2O}\, \rightleftharpoons Y + W$
correct statement is

$(I)$ $ZnCl_2$ is ionic whereas $CdCl_2$ and $HgCl_2$ are covalent
$(II)$ $Zn$ and $Cd$ dissolves in dilute acid $(HCl)$ liberating $H_2$ but $Hg$ can not
$(III)$ $Zn$ and $Cd$ forming with ppt. of $Zn(OH)_2$ and $Cd(OH)_2$ but $Hg$ forms coloured ppt. of
$(IV)$ all from $A_2^{2+}$ type ion