Question

Which of the comparison regarding $Zn,Cd,Hg$ is/are correct?

(I) $Zn{Cl}_2$ is ionic whereas $Cd{Cl}_2$ and $Hg{Cl}_2$ are covalent.

(II) $Zn$ and $Cd$ dissolves in dilute acid $\left(HCl\right)$ liberating $H_2$ whereas $Hg$ do not.

(III) $Zn$ and $Cd$ forms precipitate of $Zn(OH{)}_2$ and $Cd{\left(OH\right)}_2$ but $Hg$ forms coloured precipitate of $Hg(OH{)}_2$.

(IV) All forms $A_2^{2+}$ type ion.

• A. Only III
• B. I, III and IV
• C. II and III
• D. All of these

Answer 1

Answer: (C)

II and III

(I) Mercuric chloride is covalent in nature whereas zinc chloride and cadmium chloride are ionic in nature.
Thus, statement (I) is incorrect.
(II) Less electropositive mercury cannot displace hydrogen from acids. More electropoitive zinc and cadmium can displace hydrogen from acids.
Thus, statement (II) is correct.
(III) Mercury does not forms hydroxide or peroxide whereas zinc and cadmium forms hydroxide and peroxide.
Thus, statement (III) is correct.
(IV) Mercury forms $H{g}_2^{2+}$ which is unique as no other ion exists as such.
Zinc and cadmium does not form $A_2^{2+}$ ion.
Thus, statement (IV) is incorrect.
Thus, only statements (II) and (III) are correct.