Question

Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Answer 1

When a charged balloon (either positively or negatively charged) is brought near the balloon having same charge, it repels due to the property that same charges repel each other.
But when a charged balloon is bring in contact with the uncharged balloon, it induces charge of opposite nature into the uncharged balloon due to the property of conduction of charges. That's why they attract each other.