Question

Bohr’s model is not valid for:
(A) H-atom
(B) D-atom
(C) T-atom
(D) He-atom

Answer 1

Hint: To solve this informative illustration, we need to have a basic knowledge about the Bohr’s model of an atom.
The validity of the given atoms can be decided when we would also know the exceptions about the model as in chemistry exceptions play an important role in deciding a proof for any empirical statement.

Complete answer:
Let us study about the Bohr’s model of an atom;
Bohr’s model:
It is basically the modification of Rutherford’s model of an atom which explains that the nucleus is a positively charged species surrounded by electrons.
Bohr’s model explains that the electrons move in a fixed path called orbitals or shells and have fixed energy levels. This model concludes that, if an electron is away from the nucleus, then it will have more energy and vice versa.
In short, Bohr’s model explains the planetary motion of electrons around the nucleus. Although, this model too had its own limitations and further modifications; it was the first model to incorporate quantum theory.
The Bohr’s model of an atom is valid for hydrogen-like atoms. In short, it is valid for mono-electron species and invalid for multi-electron species. It is exactly applicable for a single electronic system and not for less than an electron too.
Thus, we can say that the Bohr’s model is applicable for H-atom (empirical), D-atom (isotope of H), T-atom (isotope of H) but not valid for He-atom (as 2 electrons are present and are not subjected to central forces).

Therefore, option (D) is correct.

Note:
Do note that Bohr’s model is valid for $H{e}^{+}$ (as it has an electron) but not for He. Similarly, it is applicable for $L{i}^{++}$ but not for $L{i}^{+}$ and Li; and so on.
Also, it is not applicable for $H^{+}$ as it is merely a proton.