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Question
In which of the following systems will the radius of the first orbit (n = 1) be minimum?
Options
Hydrogen atom
Deuterium atom
Singly ionized helium
Doubly ionized lithium
Solution
Doubly ionized lithium
For a hydrogen-like ion with Z protons in the nucleus, the radius of the nth state is given by
`rn = (n^2a_0)/Z`
Here , `a_0 = 0.53 " pm"`
For lithium,
Z = 3
Therefore, the radius of the first orbit for doubly ionised lithium will be minimum.
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