Answer:The change in temperature of the gas mixture is -68.44 K.
Explanation:
1. Temperature of the bottle when only helium gas was present :T
Pressure inside the container =P= 1.83 atm
Volume of the container = V = 2.50 L
Moles of helium gas = n = 0.458 moles
Using an Ideal gas equation:


2. Temperature of the bottle when argon gas is added into the container:T'
Pressure inside the container = P' =2.05 atm
Volume of the container = V = 2.50 L
Moles of helium gas = n' = 0.458 mol + 0.713 mol = 1.171 mol


The change in temperature will be given as:
Final temperature = Initial temperature:T' - T
53.37 k - 121.81 K = -68.44 K
The change in temperature of the gas mixture is -68.44 K.