Question

When air is filled in the balloon, the pressure and volume both increases while the temperature remains unchanged. Here, Boyle’s law is not obeyed. Why is it so?
(A) Mass of air is negligible.
(B) Mass of air does not remain constant.
(C) Air is not a perfect gas.
(D) Pressure inside the balloon is less than that of the atmospheric pressure.

Answer 1

Hint:According to Boyle’s law, the pressure exerted by a gas is inversely proportional to the volume of the gas at a fixed temperature in a closed vessel. Use this definition of Boyle’s law to get the required answer to the given question.


Complete answer:
According to Boyle’s law, the pressure exerted by a gas is inversely proportional to the volume of the gas at a fixed temperature in a closed vessel or a system.
As the system is closed, this means that the quantity of the gas cannot be changed.
When air is blown into the balloon, the system is interacting with the surroundings and the quantity of air in the balloon increases.
The mass of air inside the balloon is increasing and is not a fixed value.
However, for Boyle’s law to be obeyed, the mass of the air needs to be fixed, which does not happen in this case.
Hence, Boyle’s law is not obtained when air is filled in the balloon because mass of air does remain constant.
Thus, the correct option is B.



Note: For questions like the one given, remember the exact definition of Boyle’s law and see if the conditions are all met for the law to be obeyed. Here, the mass of air in the balloon kept on changing and was not fixed, not meeting one of the conditions for Boyle’s law to be obeyed.