JEE Main · 2020 · Shift-ImediumATOM-066

For the Balmer series, in the spectrum of H atom, v = RH\1n12 - 1n22\, the correct statements among (I) to (IV) are:…

Structure of Atom · Class 11 · JEE Main Previous Year Question

Question

For the Balmer series, in the spectrum of H atom, vˉ=RH{1n121n22}\bar{v} = R_H\left\{\frac{1}{n_1^2} - \frac{1}{n_2^2}\right\}, the correct statements among (I) to (IV) are:

(I) As wavelength decreases, the lines in the series converge. (II) The integer n1n_1 is equal to 2. (III) The lines of the longest wavelength correspond to n2=3n_2 = 3. (IV) The ionization energy of hydrogen can be calculated from the wave number of these lines.

Options
  1. a

    (I), (III), (IV)

  2. b

    (I), (II), (III)

  3. c

    (I), (II), (IV)

  4. d

    (II), (III), (IV)

Correct Answerb

(I), (II), (III)

Detailed Solution

🧠 Decoding the Balmer Truths The Balmer series is our window into the atom. It describes any electron falling to the second shell (n=2n=2). As the electron falls from higher and higher shells, it releases more energy, which means shorter wavelengths. But there's a limit—shells aren't infinite!

🗺️ The Statement Audit

  • (I) True: Spectral lines cluster (converge) as nn \to \infty. This is because the energy levels En=13.6/n2E_n = -13.6/n^2 get closer and closer near the ionization limit.
  • (II) True: By definition, the Balmer series corresponds to transitions ending at n1=2n_1 = 2.
  • (III) True: Longest wavelength = Smallest energy. The smallest jump possible to level 2 is from level 3.
  • (IV) False: These lines tell us about level n=2n=2. To calculate Ionization Energy, we need the energy required to go from n=1n=1 \to \infty (Lyman series).

The "Energy Gap" Visual Think of the energy levels as steps on a ladder. The bottom steps are far apart (121 \to 2 is huge). The top steps are tiny (100101100 \to 101 is almost nothing). That's why statement (I) is always true for any series!

⚠️ Common Traps Statement (IV) is the subtle one. You could theoretically use Balmer lines to find the Rydberg constant, and then calculate IE. But the statement implies you can read IE directly from the series wavenumber, which is incorrect.

Answer: (B)\boxed{\text{Answer: (B)}}

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For the Balmer series, in the spectrum of H atom, v = RH\1n12 - 1n22\, the correct statements among… (JEE Main 2020) | Canvas Classes