What is the force opposing gravity of earth or simply gravitational force?(We can use this to invent magic broomstick like in harry potter movies!!!..)

Gravity is the weakest force in nature but depends on the mass of the particles involved. If you use any other force (Any of the three other fundamental forces or the derivatives of them) it may be possible to defy the gravity.

We do such problems like

What amount of equal charge be given to earth and moon so that the effect of gravity is nullified. If you are in an attempt to invent a device which actively defies gravity or cancels the effect of gravity, I would suggest to go ahead.

All the best.