Do the gravitational forces obey Newton's third law of motion?

The gravitational force between two objects is $F$. How will this force change when:
$(i)$ the distance between them is reduced to half?
$(ii)$ the mass of one of the objects becomes four times?

All the planets are moving in circular orbits. What provides the necessary force for this motion and what is the direction of this force? What will happen if this force disappears suddenly?

Is it possible to shield a body from a gravitational field?

Gravitational force on an imaginary planet is six times stronger than the gravitational force of the Earth. Determine the value of acceleration due to gravity and the weight of an object of mass $50 \, kg$ on that planet.

Which is greater: the attraction of earth for $1 \,kg$ of lead or attraction of $1 \,kg$ of lead for earth?