$\overline{){\mathbf{PV}}{\mathbf{=}}{\mathbf{nRT}}}$

**Step 1. **mole fraction of He

${\mathbf{{\rm X}}}_{\mathbf{Xe}}\mathbf{=}\frac{\mathbf{4}\mathbf{\%}}{\mathbf{100}\mathbf{\%}}\left(1\right)\mathbf{=}$**0.04**

mole fraction Ne = mole fraction He

${\mathbf{{\rm X}}}_{\mathbf{Ne}\mathbf{}\mathbf{and}\mathbf{}\mathbf{H}\mathbf{3}}\mathbf{=}\frac{\mathbf{1}\mathbf{-}\mathbf{0}\mathbf{.}\mathbf{04}}{\mathbf{2}}\mathbf{=}$**0.48**

A plasma-screen TV contains thousands of tiny cells filled with a mixture of Xe, Ne, and He gases that emits light of specific wavelengths when a voltage is applied. A particular plasma cell, 0.900mm x 0.300mm x 10.0mm, contains 4.00% Xe in a 1:1 Ne:He mixture at a total pressure of 500. torr. Assumptions: In order to calculate total moles of gas and total atoms, we assumed a reasonable room temperature. Since 4.00% Xe was not defined, we conveniently assumed mole percent. The 1:1 relationship of Ne to He is assumed to be by volume and not by mass.

Calculate the number of He atoms in the cell.

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