If radius of second Bohr orbit of the He^+ ion is 105.8 pm, what is the radius of third Bohr orbit of Li^2+ ion ?

1. 158.7 Å

2. 158.7 pm

3. 15.87 pm

4. 1.587 pm

Doubtly Asked 30 Oct 2026 NEET UG 2022 Practice test neet Save WhatsApp Report

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Answer: 2. 158.7 pm

Key idea: Bohr radius \(r_n=0.529\,\dfrac{n^2}{Z}\) Å, so \(r\propto n^2/Z\).

\(\mathrm{He^+}\), n = 2: \(r=a_0\times4/2=2a_0=105.8\) pm, so \(a_0=52.9\) pm.

\(\mathrm{Li^{2+}}\), n = 3: \(r=a_0\times9/3=3a_0=158.7\) pm.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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