1. Understand STP

STP stands for Standard Temperature and Pressure. It's defined as:

* Temperature: 0°C (273.15 K)

* Pressure: 1 atm

2. Molar Volume at STP

At STP, one mole of any ideal gas occupies a volume of 22.4 liters.

3. Calculate Moles of H₂

* You have 67.2 L of H₂.

* Divide the volume by the molar volume at STP: 67.2 L / 22.4 L/mol = 3 moles of H₂

4. Calculate Atoms of Hydrogen

* One molecule of H₂ contains 2 hydrogen atoms.

* You have 3 moles of H₂.

* Use Avogadro's number (6.022 x 10²³ atoms/mol) to convert moles to atoms:

3 moles H₂ * (2 atoms H / 1 molecule H₂) * (6.022 x 10²³ molecules/mol) = 3.61 x 10²⁴ atoms of hydrogen

Therefore, there are 3.61 x 10²⁴ atoms of hydrogen in 67.2 L of H₂ at STP.