The balloon will expand because of the produced CO2 and students can see bubbling - a chemical reaction has happened.

As it ascended, and the surrounding air pressure dropped, each balloon expanded completely.

However, do be aware, as the balloon expands, it will exert a compressive force on the gas inside.

Conventional, or zero-pressure, balloons expand from the heat of the sun during the day and contract at night.

The increased force, is an increase in pressure which, in turn, stretches the rubber and makes the balloon expand.

The balloon would expand, and the dots would become farther apart.

The balloon expanded even though the dots did not move.

All throughout its ascent, the balloon has been expanding.

One ant starts moving towards another, but the balloon itself is also expanding.

It could also be the case that the balloon would expand to the point of bursting before the pressures would become equal.