A particle of mass m is placed inside a spherical shell, away from its centre. The mass of the shell is M.

The particle will move towards the centre. The particle will move away from the centre, towards the nearest wall. The particle will move towards the centre if m < M and away from the centre if m > M. The particle will remain stationary.

The particle will remain stationary.

As the gravitational field inside the shell is zero, the particle will remain stationary