Answer:
[tex]0.38\ \text{moles of He}[/tex]
Explanation:
[tex]\rho[/tex] = Density of helium at stp = 0.179 g/L
M = Molar mass of helium = 4 g/mol
V = Volume of helium = 8.4 L
Mass of helium
[tex]m=\rho V\\\Rightarrow m=0.179\times 8.4\\\Rightarrow m=1.5036\ \text{g}[/tex]
Number of moles is given by
[tex]n=\dfrac{m}{M}\\\Rightarrow n=\dfrac{1.5036}{4}\\\Rightarrow n=0.3759\approx0.38\ \text{moles of He}[/tex]
The number of moles of helium in the balloon is [tex]0.38\ \text{moles}[/tex]
