The first use of quantum theory to explain the structure of atom was made by

Options

A. Heisenberg
B. Bohr
C. Plank
D. Einstein

Explanation

To solve the question regarding who first used quantum theory to explain the structure of the atom, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**: The question asks about the first application of quantum theory to atomic structure. Quantum theory fundamentally changed our understanding of atomic and subatomic processes.

2. **Identifying Key Figures**: The key figure associated with the early application of quantum theory to atomic structure is Niels Bohr.

3. **Historical Background**: In 1913, Niels Bohr proposed a model of the atom that incorporated quantum theory. This was a significant advancement in atomic physics.

4. **Bohr's Model**: Bohr's model introduced the idea that electrons orbit the nucleus at specific distances, and that these orbits correspond to quantized energy levels. This means that electrons can only occupy certain allowed energy states.

5. **Planck's Quantum Theory**: Bohr's work was influenced by Max Planck’s quantum theory, which introduced the concept of quantization of energy. Bohr used this concept to explain the stability of atoms and the emission of spectral lines.

6. **Conclusion**: Based on the above points, we can conclude that the first use of quantum theory to explain the structure of the atom was made by Niels Bohr.

### Final Answer:
The first use of quantum theory to explain the structure of the atom was made by **Niels Bohr**.

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