Answer:
For two objects of charges q1 and q2, that are separated by a distance R, the force that each object suffers is given by the Coulomb's:
F = k*q1*q2/R^2
If both charges have the same sign, then we have a positive force, which means that the objects are "pushing" each other, then this is a repulsive force.
If instead, each object has a charge with a different sign, the force will be negative, then the objects will be pulling each other, and the force is an attractive force.
a) Whit this in mind, the two possible things that can happen if a charged object is near another charged object are:
The objects repel each other, which happens when both objects have charges with the same sign.
The objects attract each other, which happens when the objects have charges with a different sign.
b) A charged balloon most probably has a static charge (the type of charge that can be obtained by rubbing the balloon with a piece of cloth), which means that it has extra electrons, and we know that electrons have a negative charge, then we can assume that this balloon has a negative charge.
Then if we put another charged balloon (also with static charge) near our original balloon they will repel each other, this happens because both balloons have a negative charge.
