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Introduction: Max Planck's theory and Niels Bohr's atomic model were two significant contributions to the understanding of atomic structure. Planck's theory of black body radiation suggested that energy was quantized into packets called quanta, which led to the development of quantum mechanics. On the other hand, Bohr's atomic model proposed that electrons orbit the nucleus in fixed energy levels. However, Planck's theory failed to explain some of the observations made by Bohr's atomic model.

Failure to Explain Line Spectra:

- Bohr's atomic model explained the discrete lines observed in the spectra of elements.
- Each line represented an electron moving from one energy level to another.
- However, Planck's theory failed to explain the origin of these energy levels.

Failure to Explain Electron Spin:

- Bohr's atomic model did not account for the electron spin, which was discovered later.
- The spin of the electron affects its energy, and thus, should have been considered in the model.
- Planck's theory also failed to explain the phenomenon of electron spin.

Failure to Explain Wave-Particle Duality:

- Planck's theory suggested that energy was quantized into particles called quanta.
- However, experiments showed that particles also exhibit wave-like behavior.
- This wave-particle duality could not be explained by Planck's theory.

Conclusion: In conclusion, while both Max Planck's theory and Niels Bohr's atomic model made significant contributions to the understanding of atomic structure, Planck's theory failed to explain some of the observations made by Bohr's model. These failures led to the development of quantum mechanics, which incorporated both theories and provided a more comprehensive understanding of atomic structure.