Question:

The electron in hydrogen atom undergoes transition from higher orbits to an orbit of radius 476.1 pm. This transition corresponds to which of the following series?

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Remember the order of hydrogen spectral series: Lyman (1), Balmer (2), Paschen (3), Brackett (4), Pfund (5). The radius scales with \(n^2\), so \(n=3\) means \(r \approx 9 \times r_1\). Since \(r_1 \approx 0.53 \text{ \AA}\), \(9 \times 0.53 \approx 4.77 \text{ \AA}\).
Updated On: Mar 26, 2026
  • Lyman
  • Paschen
  • Balmer
  • Pfund
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The Correct Option is B

Solution and Explanation

Step 1: Formula for Radius of Orbit The radius of the \(n^{\text{th}}\) orbit of a hydrogen atom is given by: \[ r_n = 0.529 \times \frac{n^2}{Z} \ \text{\AA} \] For Hydrogen, \(Z = 1\). Given radius, \(r = 476.1 \text{ pm} = 4.761 \text{ \AA}\).
Step 2: Calculate the Orbit Number (\(n\)) Substitute the values into the formula: \[ 4.761 = 0.529 \times n^2 \] \[ n^2 = \frac{4.761}{0.529} \approx 9 \] \[ n = \sqrt{9} = 3 \] So, the electron transitions to the orbit \(n = 3\).
Step 3: Identify the Spectral Series Spectral series are defined by the final orbit (\(n_f\)) of the transition:
  • Lyman series: \(n_f = 1\)
  • Balmer series: \(n_f = 2\)
  • Paschen series: \(n_f = 3\)
  • Brackett series: \(n_f = 4\)
  • Pfund series: \(n_f = 5\)
Since the transition ends at \(n = 3\), it corresponds to the Paschen series. Final Answer:
Paschen series.
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