Since the electrons are more stable in circular path as compared to the elliptical path and this is why he assumed a circular path .. sumo dear .... it is also not fixed as any body have not show electrons to move it works only on some theory such as Schrödinger wave theory which may be proved wrong in future.

Introduction:
Niels Bohr proposed the Bohr model of the atom in 1913, which was a significant advancement in understanding the structure of atoms. One of the key features of the Bohr model was the use of circular orbits for electrons instead of elliptical orbits. This choice was based on several factors, including experimental evidence and theoretical considerations.

Experimental Evidence:
1. Spectral Lines: One of the experimental observations that influenced Bohr's choice was the discrete nature of atomic spectra. When atoms were excited and then allowed to return to their ground state, they emitted or absorbed specific wavelengths of light, resulting in characteristic spectral lines.
2. Line Intensities: The line intensities of the spectral lines could be explained by the quantization of angular momentum. Bohr proposed that the angular momentum of electrons in an atom is quantized and can only take certain discrete values.
3. Rydberg Formula: The Rydberg formula, which accurately predicted the wavelengths of spectral lines in hydrogen, provided further evidence for the quantization of angular momentum. It indicated that the angular momentum of an electron in a hydrogen atom is quantized according to the equation L = nħ, where n is an integer and ħ is the reduced Planck's constant.

Theoretical Considerations:
1. Stability: Bohr aimed to create a model that could explain the stability of atoms. He considered that electrons in elliptical orbits would be subjected to varying forces and accelerations, leading to rapid decay of their energy and ultimately collapse into the nucleus. On the other hand, electrons in circular orbits have a constant distance from the nucleus, resulting in a stable configuration.
2. Electromagnetic Radiation: Bohr incorporated the principles of classical electromagnetism into his model. According to classical electrodynamics, an accelerating charged particle emits radiation. By restricting the electron to circular orbits, Bohr minimized the acceleration of the electron, reducing the emission of electromagnetic radiation and maintaining the stability of the atom.
3. Quantization: Bohr incorporated the concept of quantization from Planck's quantum theory into his model. By postulating that the angular momentum of electrons is quantized, he could explain the discrete nature of atomic spectra and the stability of atoms.

Conclusion:
In summary, Bohr chose circular orbits over elliptical orbits in his atomic model based on experimental evidence of discrete spectral lines, line intensities, and the Rydberg formula. Theoretical considerations of stability, electromagnetic radiation, and quantization also played a crucial role in his decision. The Bohr model was a significant milestone in the understanding of atomic structure, although it was later replaced by more accurate quantum mechanical models.