Answer: 13 liters
Explanation: for this case is really important to keep in mind that 2 things that give us the conditions to proceed with this equation.
the first one is that the Temperature and pressure remain constant, so like this values are constant we do not use them to calculate the amount of volume because always will be the same.
the second one is that we are working with the same gas, so the gas does not change and conditions dos not change too. then we can proceed.
if for 1.2 mole of gas we have 8.5 liter how many we have for 0.65 mole
then we apply this equation
0.65 mole * ( 8.5 liter /1.2 mole ) = 4.25 liter
as we are working with the same gas, we only need to sum the values in liter for each amount in mole
then we get this result
8.5 liter + 4.25 liter b= 12.75 liter = 13 liter
