Final answer:
By doubling the number of moles of gas inside a balloon while keeping temperature and pressure constant, the volume of the gas in the balloon also doubles, according to Avogadro's Law.
Step-by-step explanation:
When you blow into a balloon and double the number of moles of gas while keeping the temperature and pressure constant, according to Avogadro's Law, the volume of the gas will also double. This is because Avogadro's Law states that at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of gas.
Therefore, if you start with a certain volume and you add more gas (blow into the balloon a second time with the same number of moles), the volume of the gas will increase proportionally. In this case, it is stated that the number of moles has doubled, hence the volume of the gas in the balloon will also double.