The simple Bohr model is not applicable to He4 atom because

(a) He4 is an inert gas
(b) He4 has neutrons in the nucleus
(c) He4 has one more electron
(d) electrons are not subject to central forces

1. (a, c)

2. (a, c, d)

3. (b, d)

4. (c, d)

(4) Hint: The Bohr model is only applicable to the Hilike atoms.
The simple Bohr model is not applicable to He4 atom because He4 has one more electron and electrons are not subject to central forces.