Initial pressure of a gas= 1200.0 mm Hg
Final pressure of a gas = 850.0 mm Hg
Initial volume of a gas = 85.0 mL
Final volume of a gas = 350.0 mL
Initial temperature of a gas = 90.0 °C = 90 + 273.15 = 363.15 K
Using the combined gas law we have,
P₁V₁/T₁ = P₂V₂/T₂
T₂ = P₂V₂T₁ / P₁V₁
where P₁, V₁, T₁ stands for initial pressure, volume and temperature respectively and P₂, V₂, T₂ stands for final pressure, volume and temperature respectively
Plugging the given data in the combined gas law we get,
(1200.0 mm Hg x 85.0 mL) / 363.15 K = (850.0 mm Hg x 350.0 mL)/ T₂
T₂ = (850.0 mm Hg x 350.0 mL x 363.15 K)/ (1200.0 mm Hg x 85.0 mL)
T₂ = 1059.2 K = 1059.18 - 273.15 = 786 °C
Final temperature of a gas = 786 °C
To convert °C to Fahrenheit
(°C × 9/5) + 32
(786°C × 9/5) + 32 = 1446.8 °F
Final temperature in Fahrenheit = 1446.8 °F