JEE Main 2021 — Chemistry Inorganic Chemistry

2021mcqeasy

The ionic radii of ${K}^{+},{\mathrm{Na}}^{+},{\mathrm{Al}}^{3+}$ and ${\mathrm{Mg}}^{2+}$ are in the order :

Official previous-year question

Held on 25 Jul 2021 · Verified 6 Jul 2026.

Options

A
${\mathrm{Na}}^{+}<{K}^{+}<{\mathrm{Mg}}^{2+}<{\mathrm{Al}}^{3+}$
B
${\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{K}^{+}<{\mathrm{Na}}^{+}$
C
${\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}<{K}^{+}$
D
${K}^{+}<{\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}$

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Solution

${\mathrm{Al}}^{3+},{\mathrm{Mg}}^{2+}$ and ${\mathrm{Na}}^{+}$ are isoelectronic ionic species. For monatomic ionic isoelectronic species as positive charge increases ionic size decreases.

The order of size of ${\mathrm{Na}}^{+}&{K}^{+}$ is ${\mathrm{Na}}^{+}<{K}^{+}$ ,

$\therefore$ Increasing order of ionic radii: ${\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}<{K}^{+}$

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JEE Main 2021 — Chemistry Inorganic Chemistry

2021mcqeasy

The ionic radii of ${K}^{+},{\mathrm{Na}}^{+},{\mathrm{Al}}^{3+}$ and ${\mathrm{Mg}}^{2+}$ are in the order :

Official previous-year question

Held on 25 Jul 2021 · Verified 6 Jul 2026.

Options

A
${\mathrm{Na}}^{+}<{K}^{+}<{\mathrm{Mg}}^{2+}<{\mathrm{Al}}^{3+}$
B
${\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{K}^{+}<{\mathrm{Na}}^{+}$
C
${\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}<{K}^{+}$
D
${K}^{+}<{\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}$

Did you get this right?

Solution

${\mathrm{Al}}^{3+},{\mathrm{Mg}}^{2+}$ and ${\mathrm{Na}}^{+}$ are isoelectronic ionic species. For monatomic ionic isoelectronic species as positive charge increases ionic size decreases.

The order of size of ${\mathrm{Na}}^{+}&{K}^{+}$ is ${\mathrm{Na}}^{+}<{K}^{+}$ ,

$\therefore$ Increasing order of ionic radii: ${\mathrm{Al}}^{3+}<{\mathrm{Mg}}^{2+}<{\mathrm{Na}}^{+}<{K}^{+}$

JEE Main 2021 — Chemistry Inorganic Chemistry

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JEE Main 2021 — Chemistry Inorganic Chemistry

Options

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Solution

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JEE Main Inorganic Chemistry in other years

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Physical Chemistry

Organic Chemistry

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