Question

A balloon kept in sun, after some time bursts. Why?

Answer 1

When the balloon is kept in the sun, due to Sun's heat, the kinetic energy of gaseous particles inside the balloons also gets increased and the balloon expands. This will increase the pressure on the walls of the balloon. It continues to expand and comes to a stage when the baloon bursts

Answer 2

A variety of gases are present inside a balloon. The gas molecules possess kinetic energy. So when temperature increases the kinetic energy of the gas molecules also increases. The gas molecules keep on putting pressure on the walls of the balloon. A time comes when the walls of the balloon can't withstand the increasing pressure.

After that the balloon bursts.