Chemistry · Covalent Bonding: Concept of electronegativity, Fajan's rule, dipole moment, Valence Shell Electron Pair Repulsion (VSEPR) theory and shapes of simple molecules
is thermally more stable than because:
\( Z n C O_{3} \) is thermally more stable than \( M g C O_{3} \) because:
- A. \( M g(O H)_{2} \) exhibits only basic properties while \( Z n(O H)_{2} \) is amphoteric
- B. polarising action of \( Z n^{2+} \) with 18 -electron configuration on the anion is larger than that of \( M g^{2+} \) with a noble-gas electron configuration and of same size and charge
- C. \) both (a) and (b) are correct
- D. none of the above is correct
Step-by-step solution
The given statement that ZnCO3 is thermally more stable than MgCO3 is false. In reality, ZnCO3 decomposes at a lower temperature (around 300°C) than MgCO3 (around 350°C), indicating it is less stable. This is because Zn2+ has a higher polarizing power due to its 18-electron configuration, which destabilizes the carbonate ion more than Mg2+ with a noble-gas configuration. Therefore, neither A (which discusses hydroxide properties unrelated to carbonate stability) nor B (which correctly identifies higher polarization but would imply lower stability, contradicting the premise) can be valid reasons for the false premise. Thus, none of the options are correct.