2 pie r = n lambda why
As per de Broglie's theory, electrons have wave-like characteristics.
In order for an electron to exist in a stable orbit around the nucleus, the circumference of the orbit (2πr) should be an integer number (n) times the wavelength of the electron (λ).
This allows the wave of the electron not to cancel itself out and be able to create a standing wave.
If this is not fulfilled, the wave would cancel out, and the orbit would not be stable.