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

1. Hydrogen atom
2. Doubly ionized lithium
3. Singly ionized helium
4. Deuterium atom

Correct answer: Doubly ionized lithium

Solution

The radius of the first orbit is inversely proportional to the atomic number (Z). Doubly ionized lithium (Z = 3) has the highest atomic number among the options, resulting in the smallest radius for the first orbit.

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