Answer:
The volume of the vessel is 250 L
Partial pressure of hydrogen = 189 torr
Explanation:
Using Boyle's law

Given ,
V₁ = 20.0 L
V₂ = ?
P₁ = 25 atm
P₂ = 2 atm
Using above equation as:




<u>The volume of the vessel is 250 L.</u>
According to Dalton's law of partial pressure:-

So, according to definition of mole fraction:

Also,
Mole fraction of H₂ = 1 - Mole fraction of He = 1 - 0.75 = 0.25
So,
Total pressure = 756 torr
Thus,

<u>Partial pressure of hydrogen = 189 torr.</u>