Gravitation is the phenomenon of interaction between ............

Two particles of mass $m_{1}$ and $m_{2}$ approach each other due to their mutual gravitational attraction only. Then,

Define the universal gravitational constant $(G)$.

An astronaut of mass $m$ is working on a satellite orbiting the Earth at a distance $h$ from the Earth's surface. The radius of the Earth is $R$,while its mass is $M$. The gravitational pull $F_G$ on the astronaut is

Statement $(I)$: The force of attraction due to a hollow spherical shell of uniform density on a point mass situated inside it is always zero.
Statement $(II)$: The force of attraction between a hollow spherical shell of uniform density and a point mass situated outside is the same as if the entire mass of the shell were concentrated at the center of the shell.
Which of the following is correct?

Two point objects of mass $2x$ and $3x$ are separated by a distance $r$. Keeping the distance fixed,how much mass should be transferred from $3x$ to $2x$,so that the gravitational force between them becomes maximum?