Which of the comparison regarding Zn, Cd, Hg is/are incorrect ?<br>(I) ZnCl2 is ionic whereas CdCl2 — d and f Block Elements Chemistry Question
Question
Which of the comparison regarding Zn, Cd, Hg is/are incorrect ?<br>(I) ZnCl2 is ionic whereas CdCl2 and HgCl2 are covalent<br>(II) Zn and Cd dissolves in dilute acid (HCl) liberating H2 but Hg can not<br>(III) Zn and Cd forming with ppt. of Zn(OH)2 and Cd(OH)2 but Hg forms coloured ppt. of Hg(OH)2<br>(IV) all form A2^2+ type ion
💡 Solution & Explanation
Step 1: The melting point of transition metals depends on the strength of metallic bonding, which is determined by the number of unpaired d-electrons available for delocalization. Step 2: Zinc (Zn) has a fully filled d-subshell (3d10 4s2) with zero unpaired electrons, resulting in very weak metallic bonding and a low melting point (419°C). Copper (Cu) has one 4s electron (3d10 4s1) and melts at 1085°C. Nickel (Ni) has two unpaired d-electrons (3d8 4s2) and melts at 1455°C. Iron (Fe) has four unpaired electrons (3d6 4s2) and melts at 1538°C. Step 3: Therefore, the correct order of increasing melting point is Zn < Cu < Ni < Fe, matching option (a).