A particle placed
1.inside a uniform spherical shell of mass M, but not at the center
2.inside a uniform spherical shell of mass M, at the center
3.outside a uniform spherical shell of mass M, a distance r from the center
4.outside a uniform solid sphere of mass M, a distance 2r from the center
If `F_1,F_2,F_3` and `F_4` are gravitational forces acting on the particle in four cases.

Explanation

White phosphorus is very reactive, due to the `P - P - P` bond angle strain at `60^(@)`.
Red phosphorus is very stable, due to chain like polymeric structure