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What is the expression for the wavelength λ in the Lyman series transition from n=2 to n=1?

1. 1 / λ = R [1 / (2²) - 1 / (1²)]
2. 3R / 4
3. λ = R [1 / (2²) - 1 / (1²)]
4. None of these

Correct answer: 1 / λ = R [1 / (2²) - 1 / (1²)]

Solution

The Lyman series corresponds to transitions to the n=1 energy level. Using the Rydberg formula, 1/λ = R [1/n₁² - 1/n₂²], where n₁=1 and n₂=2 for the 2 → 1 transition. This matches option A.

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