In which of the following systems will the radius of the first orbit (n = 1) be minimum? (a) doubly ionized lithium (b) singly ionized helium (c) deuterium atom (d) hydrogen atom

Answer: (a). rn = (n² a₀)/(Z), so for n = 1, r ∝ 1/Z. Li ²⁺ has Z = 3, the largest among the options (He ⁺: 2, D and H: 1). So the answer is (a) doubly ionized lithium.

In which of the following systems will the radius of the first orbit… | NEET 2003 (AIPMT)

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Bohr Model: Orbits, Speed & Angular Momentum

In which of the following systems will the radius of the first orbit (n = 1) be minimum?

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Answer: (a)

$r_n = \dfrac{n^2 a_0}{Z}$ , so for $n = 1$ , $r \propto \dfrac{1}{Z}$ .
Li $^{2+}$ has $Z = 3$ , the largest among the options (He $^+$ : 2, D and H: 1).
So the answer is (a) doubly ionized lithium.

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