Aweather balloon on the ground has a volume of 200 l at 25.0 °c when filled with helium to a pressure of 100 kpa. what is the volume of the balloon (in l) at 9000 m, where the temperature is –50.0 °c and the pressure is 19.5 kpa?

According to Gas law equations, we know, 
P₁V₁/T₁ = P₂V₂/T₂

Here, P₁ = 100 kPa
P₂ = 19.5 kPa
T₁ = 25+273 = 298k
T₂ = -50+273 = 223k
V₁ = 200 L
V₂ = ?

Substitute their values, 
100*200 / 298 = 19.5*V₂/223
20000*223 / 298*19.5 = V₂
V₂ = 4460000 / 5811
V₂ = 767.50 L

In short, Your Answer would be: 767.50 Liter

Hope this helps!

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