All of these EXCEPT helium in a balloon
<span>Boyles law states that the volume of a gas is proportional to the moles of the gas when pressure and temperature are kept constant. </span>
Answer : The final pressure of the gas will be, 26.8 kPa
Explanation :
According to the Boyle's law, the pressure of the gas is inversely proportional to the volume of the gas at constant temperature of the gas and the number of moles of gas.

or,

or,

where,
= initial pressure of the gas = 209 kPa
= final pressure of the gas = ?
= initial volume of the gas = 10.0 L
= final volume of the gas = 78.0 L
Now put all the given values in this formula, we get the final pressure of the gas.


Therefore, the final pressure of the gas will be, 26.8 kPa
Answer: D) 1.00 g
Explanation:
According to the Avogadro's law, the volume of gas is directly proportional to the number of moles of gas at same pressure and temperature. That means,

or,

where,
= initial volume of gas = 2.00 L
= final volume of gas = 3.00 L
= initial moles of gas =
= final moles of gas = ?
Now we put all the given values in this formula, we get


Mass of helium =
Thus mass of helium added = (3.00-2.00) g = 1.00 g