# Class 12 Physics MCQ – The Line Spectra of the Hydrogen Atom

This set of Class 12 Physics Chapter 12 Multiple Choice Questions & Answers (MCQs) focuses on “The Line Spectra of the Hydrogen Atom”.

1. What causes spectral lines?
a) The transition of electrons between two energy levels
b) The transition of electrons between two wavelength ranges
c) Magnetic and electric field exiting in an atom
d) The transition of electrons from electric to magnetic field

Explanation: The observed spectral lines are caused by the transition of electrons between two energy levels in an atom. The emission spectrum of the hydrogen atom is divided into many spectral series, with wavelengths that are given by Rydberg’s formula.

2. How many spectral lines are there in the hydrogen spectrum?
a) Infinity
b) Zero
c) Multiple
d) One

Explanation: Even though hydrogen has only one electron in its outermost shell, it has multiple spectral lines. This is because hydrogen has many energy levels. When the electron excites from a lower level of energy into a higher level, then it releases a photon, and this photon is the one that appears as spectral lines.

3. Which theory explained that electrons revolved in circular orbits?
a) Einstein theory
b) Bohr theory
c) Rydberg theory
d) de – Broglie theory

Explanation: Niels Bohr explained the line spectrum of the hydrogen atom with the assumption that electrons revolved around an atom in circular orbits and that the orbit closer to the nucleus represented the ground state and the farther orbits represented the higher levels of energy.

4. Bohr’s model only works for hydrogen or helium.
a) True
b) False

Explanation: Yes, this is a true statement. Bohr’s model works only for elements like hydrogen because the model only considers the interactions between one electron and the nucleus. If there are more electrons, then they will repel the one electron, and this, in turn, will change its energy level.

5. When is hydrogen stable?
a) When the electron jumps to higher energy levels
b) When an electric field is introduced
c) When a magnetic field is introduced
d) When the electron is at its ground state

Explanation: The hydrogen atom is stable when the electron rests at the ground level of energy, i.e. when the principal quantum number, n = 1. In other words, when the electron is revolving in the first orbit around the nucleus, the hydrogen atom is stable.
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6. Which of the following is found in the UV region of the spectrum?
a) Pfund series
b) Brackett series
c) Lyman series
d) Paschen series

Explanation: The transitions that end at the ground level, where the principal quantum number is one, are called the Lyman series. Here, the energies that are released are so large, and therefore, these spectral lines appear in the ultraviolet region of the spectrum.

7. How many spectral lines does hydrogen have?
a) Four
b) Three
c) Two
d) One

Explanation: Niels Bohr calculated the energies that a hydrogen atom would have in each of its energy levels, based on the wavelength of the spectral lines. Then he found out that there are four spectral lines for hydrogen, namely, Lyman, Balmer, Paschen, and Brackett series. The Lyman series lies in the UV region, whereas the Balmer series lies in the visible region, and the last two lie in the infrared region.

Sanfoundry Global Education & Learning Series – Physics – Class 12.

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