The gravitation intensity at the centre C of the drumhead defined by a hemispherical shell has the direction indicated by the arrow [see Fig. 8.46]

Explanation

We know that the gravitational potential is constant at all points inside a spherical shell. Therefore, the gravitational potential gradient at all points inside the spherical shell is zero [i.e., as `V` is constant, `(dV)/(dr) = 0`].
Since, gravitational intensity is equal to negative of the gravitational potential gradient, hence the gravitational intensity is zero at all points inside a hollow spherical shell.
This indicates that the gravitational forces acting on a particle at any point inside a spherical shell, will be symmetrtically placed.
Therefore. if we remove the upper hemispherical shell, the net gravitational force acting on the particle at the centre `Q` or at some other point `P` will be acting downwards which will also be the direction of gravitational intensity. it is so because, the gravitational intensity at a point is the gravitational force per unit mass at that point. Hence, the gravitational intensity at the centre `Q` will be also c.i.e., option (iii) is correct.