Option (iii) is the correct answer. The assertion is true because molten ionic compounds conduct electricity, but the reason is completely false because ions are fixed in solids and mobile only in liquids.
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The atomic number is 11 and mass number is 23. It is a positively charged cation because protons exceed electrons by one. Its electronic configuration is 2, 8 and the species is a sodium ion, Na+.
Option (iii) correctly represents the chloride ion Cl-. A neutral chlorine atom has 17 electrons with arrangement 2, 8, 7. Gaining one electron forms Cl- with 18 electrons distributed as 2, 8, 8 in three shells.
The resulting chemical formulae are CaBr2, Al2(CO3)3, K2SO4 and NH4Cl. In each ionic compound, the valency numbers are criss-crossed so that positive and negative charges balance out to maintain overall electrical neutrality.
(i) Aluminium nitrate has the chemical formula Al(NO3)3. (ii) Calcium oxide has the chemical formula CaO. (iii) Ferric oxide has the chemical formula Fe2O3. Each formula balances the combining valencies of the constituent ions.