What is the ratio of the gravitational force between two masses kept at a certain distance in air to the force between them when kept in any other medium?

Two objects of masses $m_1$ and $m_2$ having the same size are dropped simultaneously from heights $h_1$ and $h_2$ respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if $(i)$ one of the objects is hollow and the other one is solid and $(ii)$ both of them are hollow,size remaining the same in each case. Give reason.

Define mass and weight of an object. Write their $SI$ units. An object has a mass of $20 \, kg$ on Earth. What will be its mass and weight on the surface of the Moon? ($g$ on Moon $= 1.6 \, m s^{-2}$)

State two factors on which the value of $g$ depends.

Explain an activity to show that,during a free fall,heavier and lighter objects accelerate at the same rate.

When an object, say an apple, falls towards the Earth, the Earth rises up to meet it. Is this true? If so, why is the Earth's motion not noticeable?