KCET · Chemistry · Classification of Elements and Periodicity in Properties

Which of the following is the correct order of radius?

A \( \mathrm{H}^{-}>\mathrm{H}>\mathrm{H}^{+} \)
B \( \mathrm{Na}^{+}>\mathrm{F}^{-}>\mathrm{O}^{2-} \)
C \( \mathrm{F}^{-}>\mathrm{O}^{2-}>\mathrm{Na}^{+} \)
D \( \mathrm{Al}^{3+}>\mathrm{Mg}^{2+}>\mathrm{N}^{3-} \)

Verified Solution

Answer & Solution

Correct Answer

(A) \( \mathrm{H}^{-}>\mathrm{H}>\mathrm{H}^{+} \)

Step-by-step Solution

Detailed explanation

The size of anion is always higher than that of the parentatom due to the decrease in effective nuclear charge on anion
\( \left(Z_{\text {eff }}\right) \) while, the size of cation is always smaller than parent atom due to lesser \( \left(Z_{\text {eff }}\right) \) than parent atom. Hence, the
correct given order is \( H^{-}>H>H^{+} \)

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.

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