According to Boyle's law, at constant temperature, the volume of a given mass of gas is inversely proportional to its pressure. But when a balloon is filled with air, both volume and pressure of the gas inside it increase-explain.

Explanation

When the balloon is pumped, the quantity of air inside the balloon goes on increasing. As a result, the mass of air inside it does not remain constant. Moreover, pumping causes rise in temperature of air inside the balloon. Thus, neither the temperature nor the mass of the air remain constant. So, Boyle's law is not applicable in this case.