(i) How many orbits are possible for n=4?
(ii) What are the limitations of bohr's model of an atom?

Explanation

(i)If n=4, the possible numbers of orbitals are calculated as follows.

(ii) Limitations of Bohr.s atom model:
1. The bohr.s atom model is applicable only to species having one election such as hydrogen `Li^(2+)` etc and not applicable to multi-election atoms.
2. It was unable to elpanation the splitting of spectral lines the presence of magnetic field (zeemeffect) or an electic field (stark effect).
3. Bohr.s theory was unable to explan why the electron is restriced to revolve around the nucleus in a fixed orbit in which the anguler momentum of the electron is equal to `nh//2pi`.