Answer: 23.1 L
Explanation: To solve this problem, you can use the ideal gas law, which states that the volume of a gas is directly proportional to the number of moles of gas, as long as the temperature and pressure are kept constant. This means that if you double the number of moles of gas, the volume will also double.
You can set up the following proportion:
(volume of 1.5 mol of butane) / (volume of 2.5 mol of butane) = (1.5 mol) / (2.5 mol)
Solving for the volume of 1.5 mol of butane, we find that it is equal to (1.5 mol) / (2.5 mol) * (38.5 L) = 23.1 L.
Therefore, the volume of 1.5 mol of butane gas at constant temperature and pressure is approximately 23.1 L.