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STD 11 - 3. Classification of elements and periodicity in properties — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 11 - 3. Classification of elements and periodicity in properties4 Marks
MCQ
$A{l^{3 + }}$ has a lower ionic radius than $M{g^{2 + }}$ because
  • A
    $Mg$ atom has less number of neutrons than $Al$
  • ✓
    $A{l^{3 + }}$ has a higher nuclear charge than $M{g^{2 + }}$
  • C
    Their electronegativities are different
  • D
    $Al$ has a lower ionisation potential than $Mg$ atom
✓

Answer

Correct option: B.
$A{l^{3 + }}$ has a higher nuclear charge than $M{g^{2 + }}$
b
$Al ^{3+}$ and $Mg ^{2+}$ have equal number of electrons and are, therefore, isoelectronic.

For iso-electronic species, size depends upon the effective nuclear charge and size is inversely proportional to the effective nuclear charge. More is the positive charge, more is the effective nuclear charge and thus, lesser is the size.

Since the effective nuclear charge is greater in $Al ^{3+}$ than $Mg ^{2+}$, it has a smaller size than $Mg ^{2+}$.

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