TS EAMCET · Chemistry · Classification of Elements and Periodicity in Properties

Arrange the following in increasing order of ionic radii $\mathrm{O}^{2-}, \mathrm{Na}^{+}, \mathrm{F}^{-}, \mathrm{Mg}^{2+}$

A $\mathrm{Mg}^{2+} < \mathrm{Na}^{+} < \mathrm{F}^{-} < \mathrm{O}^{2-}$
B $\mathrm{Mg}^{2+} < \mathrm{F}^{-} < \mathrm{Na}^{+} < \mathrm{O}^{2-}$
C $\mathrm{O}^{2-} < \mathrm{F}^{-} < \mathrm{Na}^{+} < \mathrm{Mg}^{2+}$
D $\mathrm{O}^{2-} < \mathrm{Mg}^{2+} < \mathrm{F}^{-} < \mathrm{Na}^{+}$

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Answer & Solution

Correct Answer

(A) $\mathrm{Mg}^{2+} < \mathrm{Na}^{+} < \mathrm{F}^{-} < \mathrm{O}^{2-}$

Step-by-step Solution

Detailed explanation

All these ions are isoelectronic. Therefore, more negative charge leads to larger radius and more positive charge leads to shorter radius. \[ \therefore \quad \mathrm{Mg}^{2+} < \mathrm{Na}^{+} < \mathrm{F}^{-} < \mathrm{O}^{2-} \]

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Following lists contain reactions and their corresponding equilibrium constants at different temperatures:

List - I (Reaction)	List - II $(K_{p})$
$2 {SO}_{2} (g) + O_{2} (g) ⇌ 2 {SO}_{3} (g) at 298 K$	$4.0 \times 10^{24}$
$2 {SO}_{2} (g) + O_{2} (g) ⇌ 2 {SO}_{3} (g) at 700 K$	$3.0 \times 10^{4}$
$N_{2} O_{4} (g) ⇌ 2 {NO}_{2} (g) at 298 K$	$0.98$
$N_{2} O_{4} (g) ⇌ 2 {NO}_{2} (g) at 500 K$	$1700$

∆ H_{1}^{0} and ∆ H_{2}^{0}

are the standard enthalpies for the reactions

2 {SO}_{2} + O_{2} ⇌ 2 {SO}_{3} and N_{2} O_{4} ⇌ 2 {NO}_{2}

respectively, then:

TS EAMCET 2019 Easy

The correct order of rates of $\mathrm{C}-\mathrm{Br}$ bond ionisation of the following bromides is:

TS EAMCET 2019 Medium

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Arrange the following in increasing order of ionic radii \(\mathrm{O}^{2-}, \mathrm{Na}^{+}, \mathrm{F}^{-}, \mathrm{Mg}^{2+}\)

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