For which one of the following Bohr models is not valid?

1.	Singly ionised helium atom \(\big(\mathrm{He}^{+}\big).\)
2.	Deuteron atom.
3.	Singly ionised neon atom \(\big(\mathrm{Ne}^{+}\big).\)
4.	Hydrogen atom.

Atomic number of H-like atom with ionization potential \(122.4~\text{V}\) for \(n=1\) is:
1. \(1\)
2. \(2\)
3. \(3\)
4. \(4\)

What is the shortest wavelength present in the Paschen series of spectral lines?
1. \(818.9~\text{nm}\)
2. \(779~\text{nm}\)
3. \(500~\text{nm}\)
4. \(1024~\text{nm}\)

The ionisation potential of the hydrogen atom is \(13.6~\text{eV}.\) The hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy of \(12.1~\text{eV}.\) According to Bohr’s theory, the spectral lines emitted by hydrogen atoms will be:
1. two
2. three
3. four
4. one

The wavelength of the first line of the Lyman series for a hydrogen atom is equal to that of the second line of the Balmer series for a hydrogen-like ion. What is the atomic number \(Z\) of hydrogen-like ions?
1. \(4\)
2. \(1\)
3. \(2\)
4. \(3\)

What happens when an electron makes a transition from an excited state to the ground state of a hydrogen-like atom or ion?

The de-Broglie wavelength of an electron in the second orbit of a hydrogen atom is equal to: