Bohr's model of the hydrogen atom was proposed by Niels Bohr in 1913. It was an improvement over the earlier classical model and provided a more accurate description of the behavior of the electrons in the atom. The model was based on several key assumptions, which are as follows:

1. Energy of the electron in the orbit is quantized:
According to Bohr's model, electrons can only exist in certain specific energy levels or orbits around the nucleus. These energy levels are quantized, meaning they can only have certain discrete values. The energy of an electron in a particular orbit is fixed and does not change unless the electron transitions to a different orbit.

2. The electron in the orbit nearest the nucleus has the lowest energy:
In Bohr's model, the electrons are arranged in different orbits around the nucleus. The orbit closest to the nucleus, called the ground state, has the lowest energy. As the distance from the nucleus increases, the energy of the orbits also increases.

3. Electrons revolve in different orbits around the nucleus:
Bohr's model proposed that electrons revolve around the nucleus in specific circular orbits. These orbits are stable and do not emit energy, unlike what classical physics predicted. Each orbit corresponds to a specific energy level, and electrons can transition between different orbits by absorbing or emitting energy in discrete amounts.

4. The position and velocity of the electrons in the orbit cannot be determined simultaneously:
This statement, option D, is not a part of Bohr's model. It is a key principle of quantum mechanics known as Heisenberg's uncertainty principle. According to this principle, it is impossible to simultaneously determine the exact position and velocity of a subatomic particle, such as an electron. This implies that it is impossible to track the precise path of an electron as it moves around the nucleus.

The uncertainty principle is a fundamental concept in quantum mechanics and has implications for our understanding of the behavior of subatomic particles. It means that we can only know the probability of finding an electron in a particular region around the nucleus, rather than its exact position and velocity at any given moment.

In conclusion, Bohr's model of the hydrogen atom includes the quantization of electron energy, the lowest energy state for the orbit closest to the nucleus, and the existence of different orbits for electrons. However, it does not include the statement that the position and velocity of electrons in the orbit cannot be simultaneously determined. This principle is a part of Heisenberg's uncertainty principle, which is a separate concept in quantum mechanics.