Question

Will mark as Brainliest.

Answer 1

We can use combined gas law,
 PV/T = k (constant)

Where, P is the pressure of the gas, V is volume of the gas and T is the temperature of the gas in Kelvin.
For two situations, we can use that as,
P₁V₁/T₁= P₂V₂/T₂

P₁ = 795 mm Hg
V₁ =  642 mL
T₁ = (273 + 23.5) K = 296.5 K
P₂ = ? 
V₂ = 957 mL
T₂ = (273 + 31.7) K = 304.7 K

From substitution,
795 mm Hg x 642 mL / 296.5 K = P₂ x 957 mL / 304.7 K
                                              P₂ = 548.072 mm Hg                                              

760 mmHg = 1 atm
548.072 mm Hg = 1 atm x (548.072 mmHg / 760 mmHg)
                           = 0.721 atm

Pressure of Oxygen gas is 0.721 atm.

Answer is "A"

Here, we made an assumption that oxygen gas has an ideal gas behavior.