Daily answer writing · Wed, 11 Nov, 2026
Fajans' rules: falling melting points NaCl, MgCl₂, AlCl₃ and why AgCl is insoluble though NaCl dissolves
State Fajans' rules. Use them to explain: (i) the melting points NaCl 801 °C, MgCl2 714 °C, while AlCl3 sublimes at about 180 °C; (ii) AgCl is sparingly soluble in water whereas NaCl is very soluble, although Ag+ (115 pm) and Na+ (102 pm) are of nearly the same size.
Syllabus: Common to CSE Paper I, IFoS Paper I and Geo-Scientist Mains (inorganic/bonding): ionic bond, polarising power and polarisability, Fajans' rules, covalent character of ionic compounds.
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