Answer:
1 mole
Step-by-step explanation:
At Standard Temperature and Pressure (273.15 Kelvin and 1 atmosphere), 22.4 L of gas is always equal to 1 mole.
We can use the Ideal Gas Equation to explain this:

At STP, like noted above, the Pressure is 1 atmosphere (or 101,325 Pa) and 273.15 Kelvin. Using this information, we can determine that the Ideal Gas Constant, R, is 0.08206. We can now solve this equation.
