Bohr Second Postulate of Quantisation

Nice Question! In this case, the matter wouldn't even exist. Atoms will exhibit non-uniform energy levels and can easily jump between different orbitals, leading to instability in the energies. This will lead to an unstable spectra and anything would, ;t exist today in the way we know it to be.

Linear momentum refers to the motion in a straight line, from one point to another. And angular momentum is the rotational equivalent of linear momentum. Since the electrons move in circular tracks or orbitals, the angular momentum is used to calculate the movement of these electrons.

This theory simply stated that there exist stationary orbits around the nucleus in which electrons rotate without dissipating any type of energy. And if the electrons try to change their orbits, then there will be a gain or loss of energy depending on the situation.