Question

Consider the isoelectronic species, Na⁺, Mg²⁺, F⁻ and
O²⁻. The correct order of increasing length of their radii is
(a) F⁻ < O²⁻ < Mg²⁺ < Na⁺
(b) Mg²⁺ < Na⁺ < F⁻ < O²⁻
(c) O²⁻ < F⁻ < Na⁺ < Mg²⁺
(d) O²⁻ < F⁻ < Mg²⁺ < Na⁺

Answer 1

The correct order is Mg2+(12) < Na+(11) < F (10) < 02- (8).

Option (B) is correct.

Explanation:

• As we know that the ionic radii of the ions shrinks as the electrons are removed from the outer valence shell.
• This is because due to removal of electrons the positive charge increases which attracts the electrons more strongly towards it.
• Due to the immense attraction by protons on electron the size of the ions decreases.

Amongst isoelectronic ions, ionic radii decrease with increase in nuclear charge:

Mg2+(12) < Na+(11) < F (10) < 02- (8)

Thus the correct order is Mg2+(12) < Na+(11) < F (10) < 02- (8).

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