The ionic radius of $\mathrm{Na}^{+}$ion is $1.02 \stackrel{\circ}{\mathrm{~A}}$. The ionic radii (in $\stackrel{\circ}{\mathrm{A}}$ ) of $\mathrm{Mg}^{2+}$ and $\mathrm{Al}^{3+}$, respectively are:

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Classification of Elements and Periodicity

The ionic radius of

Na^{+}

ion is

1.02 A \circ

. The ionic radii (in

A \circ

) of

Mg^{2 +}

and

Al^{3 +}

, respectively are:

Answer: (C)

N a^{+}

M g^{2 +}

and

A l^{3 +}

are isoelectronic, each carrying ten electrons, while the nuclear charge rises from

11

12

13

. The same ten-electron cloud is held by a stronger nucleus at each step, so the radius must fall steadily below the

1.02

Å of

N a^{+}

. The radii of

M g^{2 +}

and

A l^{3 +}

are

0.72

Å and

0.54

Å.

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Single correct option