1. Use the Ideal Gas Law:

The ideal gas law is: PV = nRT

* P = Pressure (in atm)

* V = Volume (in liters)

* n = Number of moles

* R = Ideal gas constant (0.0821 L·atm/mol·K)

* T = Temperature (in Kelvin)

2. Determine the Conditions at STP:

* STP (Standard Temperature and Pressure) is defined as:

* Temperature: 0°C = 273.15 K

* Pressure: 1 atm

3. Calculate the Number of Moles (n):

* Plug the values into the ideal gas law:

(1 atm) * (10.0 L) = n * (0.0821 L·atm/mol·K) * (273.15 K)

* Solve for n:

n = (1 atm * 10.0 L) / (0.0821 L·atm/mol·K * 273.15 K) ≈ 0.446 moles of Xe

4. Convert Moles to Atoms:

* Use Avogadro's number (6.022 x 10^23 atoms/mol) to convert moles to atoms:

0.446 moles Xe * (6.022 x 10^23 atoms/mol) ≈ 2.68 x 10^23 Xe atoms

Therefore, there are approximately 2.68 x 10^23 xenon atoms in 10.0 liters of Xe gas at STP.